Details of a Researcher - TSUJIKAWA, Shinji

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TSUJIKAWA, Shinji

Scopus Paper Info

Paper Count: 255 Citation Count: 28243 h-index: 71

Click to view the Scopus page. The data was downloaded from Scopus API in July 22, 2025, via http://api.elsevier.com and http://www.scopus.com .

Affiliation

Faculty of Science and Engineering, School of Advanced Science and Engineering

Job title

Professor

Degree

Doctor of Science ( 2001.03 Waseda University )

Homepage URL

https://tsujikawa.w.waseda.jp/Tsujikawae.html

Research Experience

2020.04

-

Now

Waseda University School of Advanced Science and Engineering Department of Physics Professor
2015.04

-

2020.03

Tokyo University of Science Faculty of Science, Division 2 Physics Professor
2008

-

2015

Tokyo University of Science Associate professor
2004

-

2008

Gunma National College of Technology Lecturer
2003

-

2004

University of Portsmouth (United Kingdom) Research associate
2001

-

2003

University of Tokyo Research associate
1999

-

2001

Waseda University Assistant professor

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Education Background

1998.04

-

2001.03

Waseda University Graduate School of Science and Engineering Doctor's Course Department of Physics and Applied Physics
1996.04

-

1998.03

Waseda University Graduate School of Science and Engineering Master's Course Department of Physics
1992.04

-

1996

The University of Tokyo Faculty of Science Department of Mathematics

Committee Memberships

2020.03

-

Now

Japanese General Relativity and Gravitation (JGRG) Organizing Committee
2014.03

-

Now

Korea-Japan Workshop on Dark Energy Organizing Committee
2012.03

-

Now

International Journal of Modern Physics D Editor
2012.03

-

Now

現代物理学に関する国際雑誌 D 学会誌及び論文誌の編集者
2011.07

-

Now

Galaxies Editor
2011.07

-

Now

論文誌 ``銀河'' 学会誌及び論文誌の編集者
2009.11

-

2011.10

日本物理学会学会誌及び論文誌の編集者

▼display all

Professional Memberships

　

　

　

Galaxies
　

　

　

International Journal of Modern Physics D
　

　

　

The physical society of Japan

Research Areas

Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics Inflation, Reheating, Quantum gravity, Cosmological perturbations, Cosmic microwave background, Dark energy, Dark matter, Large-scale structures, Black holes, Neutron stars, Gravitational waves, Extended theories of gravity

Research Interests

Cosmology, Relativity

Awards

Minister's Prize for Science and Technology (Research Category)

2025.04 Ministry of Education, Culture, Sports, Science and Technology Research on a comprehensive cosmological model from the origin of the Universe to its current accelerated expansion

Winner： Shinji Tsujikawa
PASJ Excellent Award

2019.03 The Astronomical Society of Japan Pioneering research on testing theories of gravity based on high-redshift galaxy surveys

Winner： Shinji Tsujikawa, Teppei Okumura, Others
Tokyo University of Science Outstanding Researcher Special Award

2016.03 Tokyo University of Science
Highly Cited Researchers

2014.07 Thomson Reuters Achievement of publishing highly cited papers that rank within the top 1% worldwide

Winner： Shinji Tsujikawa

Papers

Forecast constraints on the axion-photon coupling from interstellar medium heating

Makoto Amakawa, Tomohiro Fujita, Shinji Tsujikawa

Physics Letters B 866 139574 - 139574 2025.07 [Refereed]

DOI

Scopus
Nonsingular black holes and spherically symmetric objects in nonlinear electrodynamics with a scalar field

Antonio De Felice, Shinji Tsujikawa

Physical Review D 111 ( 6 ) 2025.03 [Refereed]

DOI
Instability of Nonsingular Black Holes in Nonlinear Electrodynamics

Antonio De Felice, Shinji Tsujikawa

Physical Review Letters 134 ( 8 ) 2025.02 [Refereed]

DOI
Proving the absence of large one-loop corrections to the power spectrum of curvature perturbations in transient ultra-slow-roll inflation within the path-integral approach

Ryodai Kawaguchi, Shinji Tsujikawa, Yusuke Yamada

Journal of High Energy Physics 2024 ( 12 ) 2024.12 [Refereed]

　View Summary

Abstract

We revisit one-loop corrections to the power spectrum of curvature perturbations ζ in an inflationary scenario containing a transient ultra-slow-roll (USR) period. In ref. [1], it was argued that one-loop corrections to the power spectrum of ζ can be larger than the tree-level one within the parameter region generating the seeds of primordial black holes during the USR epoch, which implies the breakdown of perturbation theory. We prove that this is not the case by using a master formula for one-loop corrections to the power spectrum obtained in ref. [2]. We derive the same formula within the path-integral formalism, which is simpler than the original derivation in [2]. To show the smallness of one-loop corrections, the consistency relations and the effective constancy of tree-level mode functions of ζ for super-Hubble modes play essential roles, with which the master formula gives a simple expression for one-loop corrections. For concreteness, we provide a reduced set of interactions including the leading-order one, while establishing the consistency relations in a self-consistent manner. We also show how the consistency relations of various operators hold explicitly, which plays a key role in proving the absence of large one-loop corrections.

DOI
Low-scale inflationary magnetogenesis without baryon isocurvature problem

Kazuki Yanagihara, Fumio Uchida, Tomohiro Fujita, Shinji Tsujikawa

Physical Review D 110 ( 8 ) 2024.10 [Refereed]

DOI
Scrutinizing black hole stability in cubic vector Galileon theories

Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2024 ( 10 ) 072 - 072 2024.10 [Refereed]

　View Summary

Abstract

In a subclass of generalized Proca theories where a cubic vector Galileon term breaks the U(1) gauge invariance, it is known that there are static and spherically symmetric black hole (BH) solutions endowed with nonvanishing temporal and longitudinal vector components. Such hairy BHs are present for a vanishing vector-field mass (m=0) with a non-zero cubic Galileon coupling β ₃. We study the linear stability of those hairy BHs by considering even-parity perturbations in the eikonal limit. In the angular direction, we show that one of the three dynamical perturbations has a nontrivial squared propagation speed c _Ω,1 ², while the other two dynamical modes are luminal.We could detect two different unstable behaviors of perturbations in all the parameter spaces of hairy asymptotically flat BH solutions we searched for. In the first case, an angular Laplacian instability on the horizon is induced by negative c _Ω,1 ². For the second case, it is possible to avoid this horizon instability, but in such cases, the positivity of c _Ω,1 ² is violated at large distances. Hence these hairy BHs are generally prone to Laplacian instabilities along the angular direction in some regions outside the horizon. Moreover, we also encounter a pathological behavior of the radial propagation speeds c _r possessing two different values of c _r ² for one of the dynamical perturbations. Introducing the vector-field mass m to cubic vector Galileons, however, we show that the resulting no-hair Schwarzschild BH solution satisfies all the linear stability conditions in the small-scale limit, with luminal propagation speeds of three dynamical even-parity perturbations.

DOI

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1

Citation

(Scopus)
Roles of boundary and equation-of-motion terms in cosmological correlation functions

Ryodai Kawaguchi, Shinji Tsujikawa, Yusuke Yamada

Physics Letters B 856 138962 - 138962 2024.09 [Refereed]

DOI

Scopus

7

Citation

(Scopus)
Revisiting linear stability of black hole odd-parity perturbations in Einstein-Aether gravity

Shinji Mukohyama, Shinji Tsujikawa, Anzhong Wang

Physical Review D 110 ( 4 ) 2024.08 [Refereed]

DOI
Probing the signature of axions through the quasinormal modes of black holes

Antonio De Felice, Shinji Tsujikawa

Physics Letters B 855 138808 - 138808 2024.08 [Refereed]

DOI

Scopus

4

Citation

(Scopus)
Even- and odd-parity stabilities of black holes in Einstein-Aether gravity

Antonio De Felice, Shinji Mukohyama, Shinji Tsujikawa, Anzhong Wang, Chao Zhang

Journal of Cosmology and Astroparticle Physics 2024 ( 08 ) 056 - 056 2024.08 [Refereed]

　View Summary

Abstract

In Einstein-Aether theories with a timelike unit vector field, we study the linear stability of static and spherically symmetric black holes against both even- and odd-parity perturbations.For this purpose, we formulate a gauge-invariant black hole perturbation theory in the background Aether-orthogonal frame where the spacelike property of hypersurfaces orthogonal to the timelike Aether field is always maintained even inside the metric horizon. Using a short-wavelength approximation with large radial and angular momenta, we show that, in general, there are three dynamical degreesof freedom arising from the even-parity sector besides two propagating degrees of freedom present in the odd-parity sector. The propagation speeds of even-parity perturbations and their no-ghost conditions coincide with those of tensor, vector, and scalar perturbations on the Minkowski background, while the odd sector contains tensor and vector modes with the same propagation speeds as those in the even-parity sector (and hence as those on the Minkowski background).Thus, the consistent study of black hole perturbations in the Aether-orthogonal frame on static and spherically symmetric backgrounds does not add new small-scale stability conditions to those known for the Minkowski background in the literature.

DOI

Scopus
Linear stability of vector Horndeski black holes

Che-Yu Chen, Antonio De Felice, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2024 ( 07 ) 022 - 022 2024.07 [Refereed]

　View Summary

Abstract

Horndeski's vector-tensor (HVT) gravity is described by a Lagrangian in which the field strength f_μν=∂_μA_ν-∂_νA_μ of a vector fieldA_μinteracts with a double dual Riemann tensorL^μναβin the form βL^μναβF_μνF_αβ, whereβis a constant. In Einstein-Maxwell-HVT theory, there are static and spherically symmetric black hole (BH) solutions with electric or magnetic charges, whose metric components are modified from those in the Reissner-Nordström geometry. The electric-magnetic duality of solutions is broken even at the background level by the nonvanishing coupling constantβ. We compute a second-order action of BH perturbations containing both the odd- and even-parity modes and show that there are four dynamical perturbations arising from the gravitational and vector-field sectors. We derive all the linear stability conditions associated with the absence of ghosts and radial/angular Laplacian instabilities for both the electric and magnetic BHs. These conditions exhibit the difference between the electrically and magnetically charged cases by reflecting the breaking of electric-magnetic duality at the level of perturbations. In particular, the four angular propagation speeds in the large-multipole limit are different from each other for both the electric and magnetic BHs. This suggests the breaking of eikonal correspondence between the peak position of at least one of the potentials of dynamical perturbations and the radius of photon sphere. For the electrically and magnetically charged cases, we elucidate parameter spaces of the HVT coupling and the BH charge in which the BHs without naked singularities are linearly stable.

DOI

Scopus
Gravitational-wave constraints on scalar-tensor gravity from a neutron star and black-hole binary GW200115

Hiroki Takeda, Shinji Tsujikawa, Atsushi Nishizawa

Physical Review D 109 ( 10 ) 2024.05 [Refereed]

DOI
Angular and radial stabilities of spontaneously scalarized black holes in the presence of scalar-Gauss-Bonnet couplings

Masato Minamitsuji, Shinji Mukohyama, Shinji Tsujikawa

Physical Review D 109 ( 10 ) 2024.05 [Refereed] [International journal]

DOI
Can we distinguish black holes with electric and magnetic charges from quasinormal modes?

Antonio De Felice, Shinji Tsujikawa

Physical Review D 109 ( 8 ) 2024.04 [Refereed]

DOI
Observational constraints on interactions between dark energy and dark matter with momentum and energy transfers

Xiaolin Liu, Shinji Tsujikawa, Kiyotomo Ichiki

Physical Review D 109 ( 4 ) 2024.02 [Refereed]

DOI
Starobinsky inflation with a quadratic Weyl tensor

Antonio De Felice, Ryodai Kawaguchi, Kotaro Mizui, Shinji Tsujikawa

Physical Review D 108 ( 12 ) 2023.12 [Refereed]

DOI
Stability of Schwarzshild black holes in quadratic gravity with Weyl curvature domination

Antonio De Felice, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2023 ( 10 ) 004 - 004 2023.10 [Refereed]

　View Summary

Abstract

We study the linear stability of static and spherically symmetric (SSS)black holes (BHs) in the presence of a Weyl-squared curvaturebesides an Einstein-Hilbert term in the action.In this theory, there is always an exact Schwarzschild BHirrespective of the Weyl coupling constant α,with the appearance of a non-Schwarzschild solutionfor a particular range of the coupling oforder |α| ≈ r _h ² (where r _h isthe horizon radius).On the SSS background, we show that the propagating degreesof freedom (DOFs) are three in the odd-parity sector and fourin the even-parity sector. Since the number of total seven DOFs coincides with those on the Minkowski and isotropic cosmological backgrounds, the Weyl gravity does not pose a strong coupling problem associated with the vanishing kinetic term of dynamical perturbations.The odd-parity perturbations possess at least one ghost mode,but the propagation speeds of all three dynamical modesare luminal.In the even-parity sector, our analysis, based on the WKB approximation, shows that, besides the appearance of at least one ghost mode, the Schwarzschild solution is prone to both radial and angular Laplacian instabilities of several dynamical perturbations for the Weyl coupling in the range |α| ≫ r _h ².For large radial and angular momentum modes, the time scales of such instabilities are much shorter than the horizon distance r _h divided by the speed of light.In the coupling regime |α|≲ r _h ², the WKB approximation does not hold any longer, and a different analysis should be performedif one wants to state the stability of both the Schwarzschild andnon-Schwarzschild BH solutions in this range of model parameters.

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4

Citation

(Scopus)
Coupled vector Gauss-Bonnet theories and hairy black holes

Katsuki Aoki, Shinji Tsujikawa

Physics Letters B 843 138022 - 138022 2023.08 [Refereed]

DOI

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5

Citation

(Scopus)
Constraining Horndeski theory with gravitational waves from coalescing binaries

Miguel Quartin, Shinji Tsujikawa, Luca Amendola, Riccardo Sturani

Journal of Cosmology and Astroparticle Physics 2023 ( 08 ) 049 - 049 2023.08 [Refereed]

　View Summary

Abstract

In the broad subclass of Horndeski theories with a luminal speed of gravitational waves, we derive gravitational waveforms emitted from a compact binary by considering the wave propagation on a spatially flat cosmological background. A scalar field nonminimally coupled to gravity gives rise to hairy neutron star (NS) solutions with a nonvanishing scalar charge, whereas black holes (BHs) do not have scalar hairs in such theories. A binary system containing at least one hairy neutron star modifies the gravitational waveforms in comparison to those of the BH-BH binary. Using the tensor gravitational waveforms, we forecast the constraints on a parameter characterizing the difference of scalar charges of NS-BH or NS-NS binaries for Advanced LIGO and Einstein Telescope. We illustrate how these constraints depend on redshift and signal-to-noise ratio, and on different possible priors. We show that in any case it is possible to constrain the scalar charge precisely, so that some scalarized NS solutions known in the literature can be excluded.

DOI

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8

Citation

(Scopus)
Black holes in a new gravitational theory with trace anomalies

Shinji Tsujikawa

Physics Letters B 843 138054 - 138054 2023.08 [Refereed]

DOI

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6

Citation

(Scopus)
Excluding static and spherically symmetric black holes in Einsteinian cubic gravity with unsuppressed higher-order curvature terms

Antonio De Felice, Shinji Tsujikawa

Physics Letters B 843 138047 - 138047 2023.08 [Refereed]

DOI

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9

Citation

(Scopus)
Black hole perturbations in Maxwell-Horndeski theories

Ryotaro Kase, Shinji Tsujikawa

Physical Review D 107 ( 10 ) 2023.05 [Refereed]

DOI
Symmetry restoration in the vicinity of neutron stars with a nonminimal coupling

Masato Minamitsuji, Shinji Tsujikawa

Physics Letters B 840 137869 - 137869 2023.05 [Refereed]

DOI

Scopus

2

Citation

(Scopus)
Primordial black holes from Higgs inflation with a Gauss-Bonnet coupling

Ryodai Kawaguchi, Shinji Tsujikawa

Physical Review D 107 ( 6 ) 2023.03 [Refereed]

DOI
Cosmological stability in f(phi,G) gravity

Shinji Tsujikawa

Physics Letters B 838 137751 - 137751 2023.03 [Refereed]

DOI

Scopus

7

Citation

(Scopus)
Cosmology in theories with spontaneous scalarization of neutron stars

Ratchaphat Nakarachinda, Sirachak Panpanich, Shinji Tsujikawa, Pitayuth Wongjun

Physical Review D 107 ( 4 ) 2023.02 [Refereed]

DOI
Inspiral gravitational waveforms from compact binary systems in Horndeski gravity

Yurika Higashino, Shinji Tsujikawa

Physical Review D 107 ( 4 ) 2023.02 [Refereed]

DOI
Instability of hairy black holes in regularized 4-dimensional Einstein-Gauss-Bonnet gravity

Shinji Tsujikawa

Physics Letters B 833 137329 - 137329 2022.10 [Refereed]

DOI

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8

Citation

(Scopus)
Stability of neutron stars in Horndeski theories with Gauss-Bonnet couplings

Masato Minamitsuji, Shinji Tsujikawa

Physical Review D 106 ( 6 ) 2022.09 [Refereed]

DOI
Probing modified gravity with integrated Sachs-Wolfe CMB and galaxy cross-correlations

Joshua A. Kable, Giampaolo Benevento, Noemi Frusciante, Antonio De Felice, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2022 ( 09 ) 002 - 002 2022.09 [Refereed]

　View Summary

Abstract

We use the cross-correlation power spectrum of the integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB) temperature anisotropy and galaxy fluctuations to probe the physics of late-time cosmic acceleration. For this purpose, we focus on three models of dark energy that belong to a sub-class of Horndeski theories with the speed of gravity equivalent to that of light: Galileon Ghost Condensate (GGC), Generalized Cubic Covariant Galileon (GCCG), and K-mouflage. In the GGC and GCCG models, the existence of cubic-order scalar self-interactions allows a possibility for realizing negative ISW-galaxy cross-correlations, while the K-mouflage model predicts a positive correlation similar to the Λ-cold-dark-matter (ΛCDM) model. In our analysis, we fix the parameters of each model to their best-fit values derived from a baseline likelihood analysis with observational data from CMB, baryon acoustic oscillations, and supernovae type Ia. Then we fit those best-fit models to the ISW-galaxy cross-correlation power spectrum extracted from a collection of photometric redshift surveys. We find that both GGC and GCCG best-fit models degrade the fit to the ISW-galaxy cross-correlation data compared to ΛCDM best-fit model. This is attributed to the fact that, for their best-fit values constrained from the baseline likelihood, the cubic-order scalar self-interaction gives rise to suppressed ISW tails relative to ΛCDM. The K-mouflage best-fit model is largely degenerate with the ΛCDM best-fit model and has a positively correlated ISW-galaxy power close to that of ΛCDM.

DOI

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9

Citation

(Scopus)
Linear stability of black holes with static scalar hair in full Horndeski theories: Generic instabilities and surviving models

Masato Minamitsuji, Kazufumi Takahashi, Shinji Tsujikawa

Physical Review D 106 ( 4 ) 2022.08 [Refereed]

DOI
Linear stability of black holes in shift-symmetric Horndeski theories with a time-independent scalar field

Masato Minamitsuji, Kazufumi Takahashi, Shinji Tsujikawa

Physical Review D 105 ( 10 ) 2022.05 [Refereed]

DOI
Relativistic star perturbations in Horndeski theories with a gauge-ready formulation

Ryotaro Kase, Shinji Tsujikawa

Physical Review D 105 ( 2 ) 2022.01 [Refereed]

DOI
Probing elastic interactions in the dark sector and the role of S_8

Jose Beltrán Jiménez, Dario Bettoni, David Figueruelo, Florencia Anabella Teppa Pannia, Shinji Tsujikawa

Physical Review D 104 ( 10 ) 2021.11 [Refereed]

DOI
Odd-parity stability of black holes in Einstein-aether gravity

Shinji Tsujikawa, Chao Zhang, Xiang Zhao, Anzhong Wang

Physical Review D 104 ( 6 ) 2021.09 [Refereed]

DOI
J-PAS: forecasts on interacting vacuum energy models

V. Salzano, C. Pigozzo, M. Benetti, H.A. Borges, R. von Marttens, S. Carneiro, J.S. Alcaniz, J.C. Fabris, S. Tsujikawa, N. Benítez, S. Bonoli, A.J. Cenarro, D. Cristóbal-Hornillos, R.A. Dupke, A. Ederoclite, C. López-Sanjuan, A. Marín-Franch, V. Marra, M. Moles, C. Mendes de Oliveira, L. Sodré Jr, K. Taylor, J. Varela, H. Vázquez Ramió

Journal of Cosmology and Astroparticle Physics 2021 ( 09 ) 033 - 033 2021.09 [Refereed]

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17

Citation

(Scopus)
Spontaneous scalarization of charged stars

Masato Minamitsuji, Shinji Tsujikawa

Physics Letters B 820 136509 - 136509 2021.09 [Refereed]

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5

Citation

(Scopus)
Cosmological perturbations for ultralight axionlike particles in a state of Bose-Einstein condensate

Shinji Tsujikawa

Physical Review D 103 ( 12 ) 2021.06 [Refereed]

DOI
Velocity-dependent interacting dark energy and dark matter with a Lagrangian description of perfect fluids

Jose Beltrán Jiménez, Dario Bettoni, David Figueruelo, Florencia A. Teppa Pannia, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2021 ( 03 ) 085 - 085 2021.03 [Refereed]

　View Summary

Abstract

We consider a cosmological scenario where the dark sector is described by two perfect fluids that interact through a velocity-dependent coupling. This coupling gives rise to an interaction in the dark sector driven by the relative velocity of the components, thus making the background evolution oblivious to the interaction and only the perturbed Euler equations are affected at first order. We obtain the equations governing this system with the Schutz-Sorkin Lagrangian formulation for perfect fluids and derive the corresponding stability conditions to avoid ghosts and Laplacian instabilities. As a particular example, we study a model where dark energy behaves as a radiation fluid at high redshift while it effectively becomes a cosmological constant in the late Universe. Within this scenario, we show that the interaction of both dark components leads to a suppression of the dark matter clustering at late times. We also argue the possibility that this suppression of clustering together with the additional dark radiation at early times can simultaneously alleviate the σ₈ and H₀ tensions.

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21

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(Scopus)
Detection of isotropic cosmic birefringence and its implications for axionlike particles including dark energy

Tomohiro Fujita, Kai Murai, Hiromasa Nakatsuka, Shinji Tsujikawa

Physical Review D 103 ( 4 ) 2021.02 [Refereed]

DOI
Instability of compact stars with a nonminimal scalar-derivative coupling

Ryotaro Kase, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2021 ( 1 ) 2021.01 [Refereed]

DOI

Scopus

8

Citation

(Scopus)
General formulation of cosmological perturbations in scalar-tensor dark energy coupled to dark matter

Ryotaro Kase, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2020 ( 11 ) 2020.11 [Refereed]

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17

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(Scopus)
Stability of relativistic stars with scalar hairs

Ryotaro Kase, Rampei Kimura, Seiga Sato, Shinji Tsujikawa

Physical Review D 102 ( 8 ) 2020.10 [Refereed]

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17

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(Scopus)
Suppressed cosmic growth in coupled vector-tensor theories

Antonio De Felice, Shintaro Nakamura, Shinji Tsujikawa

Physical Review D 102 ( 6 ) 2020.09 [Refereed]

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17

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(Scopus)
Neutron stars with a generalized Proca hair and spontaneous vectorization

Ryotaro Kase, Masato Minamitsuji, Shinji Tsujikawa

Physical Review D 102 ( 2 ) 2020.07 [Refereed]

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36

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(Scopus)
Scaling solutions and weak gravity in dark energy with energy and momentum couplings

Luca Amendola, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2020 ( 6 ) 2020.06 [Refereed]

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25

Citation

(Scopus)
Weak cosmic growth in coupled dark energy with a Lagrangian formulation

Ryotaro Kase, Shinji Tsujikawa

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 804 2020.05 [Refereed]

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27

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(Scopus)
Scalar-field dark energy nonminimally and kinetically coupled to dark matter

Ryotaro Kase, Shinji Tsujikawa

Physical Review D 101 ( 6 ) 2020.03 [Refereed]

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43

Citation

(Scopus)
Neutron stars in f(R) gravity and scalar-tensor theories

Ryotaro Kase, Shinji Tsujikawa

J COSMOL ASTROPART P 09 ( 054 ) 1 - 25 2019.09 [Refereed]

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36

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(Scopus)
Cosmological data favor Galileon ghost condensate over ΛCDM

Simone Peirone, Giampaolo Benevento, Noemi Frusciante, Shinji Tsujikawa

PHYS REV D 100 ( 063540 ) 1 - 6 2019.09 [Refereed]

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44

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(Scopus)
Cosmological constraints and phenomenology of a beyond-Horndeski model

Simone Peirone, Giampaolo Benevento, Noemi Frusciante, Shinji Tsujikawa

PHYS REV D 100 ( 063509 ) 1 - 17 2019.09 [Refereed]

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15

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Lunar laser ranging constraints on nonminimally coupled dark energy and standard sirens

Shinji Tsujikawa

PHYS REV D 100 ( 043510 ) 1 - 18 2019.08 [Refereed]

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18

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(Scopus)
Anisotropic 2-form dark energy

Juan P. Beltran Almeida, Alejandro Guarnizo, Ryotaro Kase, Shinji Tsujikawa, Cesar A. Valenzuela-Toledo

PHYS LETT B 793 ( 10 ) 396 - 404 2019.06 [Refereed]

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23

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Constraints on massive vector dark energy models from integrated Sachs-Wolfe-galaxy cross-correlations

Shintaro Nakamura, Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 99 ( 063533 ) 1 - 18 2019.03 [Refereed]

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25

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Anisotropic inflation with coupled p−forms

Juan P. Beltran Almeida, Alejandro Guarnizo, Ryotaro Kase, Shinji Tsujikawa, Cesar A. Valenzuela-Toledo

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 03 ( 025 ) 1 - 24 2019.03 [Refereed]

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18

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(Scopus)
Dark energy in Horndeski theories after GW170817: A review

Ryotaro Kase, Shinji Tsujikawa

INTERNATIONAL JOURNAL OF MODERN PHYSICS D 05 ( 1942005 ) 1 - 78 2019.02 [Refereed] [Invited]

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167

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Coupled vector dark energy

Shintaro Nakamura, Ryotaro Kase, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2019 ( 12 ) 2019 [Refereed]

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18

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Tracker and scaling solutions in DHOST theories

Noemi Frusciante, Ryotaro Kase, Kazuya Koyama, Shinji Tsujikawa, Daniele Vernieri

PHYSICS LETTERS B 790 167 - 175 2019.01 [Refereed]

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30

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Inflation with mixed helicities and its observational imprint on CMB

Lavinia Heisenberg, Hector Ramirez, Shinji Tsujikawa

PHYSICAL REVIEW D 99 ( 023505 ) 1 - 14 2019.01 [Refereed]

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3

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(Scopus)
Most general cubic-order Horndeski Lagrangian allowing for scaling solutions and the application to dark energy

Noemi Frusciante, Ryotaro Kase, Nelson J. Nunes, Shinji Tsujikawa

PHYSICAL REVIEW D 98 ( 123517 ) 1 - 17 2018.12 [Refereed]

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18

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Gauge-ready formulation of cosmological perturbations in scalar-vector-tensor theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 98 ( 123504 ) 1 - 25 2018.12 [Refereed]

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12

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Dark energy in scalar-vector-tensor theories

Ryotaro Kase, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 11 ( 024 ) 1 - 34 2018.11 [Refereed]

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19

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New scaling solutions in cubic Horndeski theories

Ines S. Albuquerque, Noemi Frusciante, Nelson J. Nunes, Shinji Tsujikawa

PHYSICAL REVIEW D 98 ( 064038 ) 1 - 17 2018.09 [Refereed]

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20

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Black holes in quartic-order beyond-generalized Proca theories

Ryotaro Kase, Masato Minamitsuji, Shinji Tsujikawa

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 782 541 - 550 2018.07 [Refereed]

　View Summary

The generalized Proca theories with second-order equations of motion can be healthily extended to a more general framework in which the number of propagating degrees of freedom remains unchanged. In the presence of a quartic-order nonminimal coupling to gravity arising in beyond-generalized Proca theories, the speed of gravitational waves ct on the Friedmann–Lemaître–Robertson–Walker (FLRW) cosmological background can be equal to that of light c under a certain condition. By using this condition alone, we show that the speed of gravitational waves in the vicinity of static and spherically symmetric black holes is also equivalent to c for the propagation of odd-parity perturbations along both radial and angular directions. As a by-product, the black holes arising in our beyond-generalized Proca theories are plagued by neither ghost nor Laplacian instabilities against odd-parity perturbations. We show the existence of both exact and numerical black hole solutions endowed with vector hairs induced by the quartic-order coupling.

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22

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Cosmology in scalar-vector-tensor theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 98 ( 024038 ) 1 - 15 2018.07 [Refereed]

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31

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(Scopus)
Odd-parity stability of hairy black holes in U(1) gauge-invariant scalar-vector-tensor theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 97 ( 124043 ) 1 - 14 2018.06 [Refereed]

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12

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Dark energy scenario consistent with GW170817 in theories beyond Horndeski gravity

Ryotaro Kase, Shinji Tsujikawa

Physical Review D 97 ( 10 ) 1 - 19 2018.05 [Refereed]

　View Summary

The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are the general scheme of scalar-tensor theories allowing the possibility for realizing the tensor propagation speed ct equivalent to 1 on the isotropic cosmological background. We propose a dark energy model in which the late-time cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the ghost condensate with cubic and quartic Galileons in the framework of GLPV theories. We show that a wide variety of the variation of the dark energy equation of state wDE including the entry to the region wDE&lt
-1 can be realized without violating conditions for the absence of ghosts and Laplacian instabilities. The approach to the tracker equation of state wDE=-2 during the matter era, which is disfavored by observational data, can be avoided by the existence of a quadratic k-essence Lagrangian X2. We study the evolution of nonrelativistic matter perturbations for the model ct2=1 and show that the two quantities μ and Σ, which are related to the Newtonian and weak lensing gravitational potentials respectively, are practically equivalent to each other, such that μ≃Σ&gt
1. For the case in which the deviation of wDE from -1 is significant at a later cosmological epoch, the values of μ and Σ tend to be larger at low redshifts. We also find that our dark energy model can be consistent with the bounds on the deviation parameter αH from Horndeski theories arising from the modification of gravitational law inside massive objects.

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51

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(Scopus)
Hairy black hole solutions in U(1) gauge-invariant scalar–vector–tensor theories

Lavinia Heisenberg, Shinji Tsujikawa

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 780 638 - 646 2018.05 [Refereed]

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25

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Relativistic stars in vector-tensor theories

Ryotaro Kase, Masato Minamitsuji, Shinji Tsujikawa

Physical Review D 97 ( 8 ) 1 - 17 2018.04 [Refereed]

　View Summary

We study relativistic star solutions in second-order generalized Proca theories characterized by a U(1)-breaking vector field with derivative couplings. In the models with cubic and quartic derivative coupling, the mass and radius of stars become larger than those in general relativity for negative derivative coupling constants. This phenomenon is mostly attributed to the increase of star radius induced by a slower decrease of the matter pressure compared to general relativity. There is a tendency that the relativistic star with a smaller mass is not gravitationally bound for a low central density and hence is dynamically unstable, but that with a larger mass is gravitationally bound. On the other hand, we show that the intrinsic vector-mode couplings give rise to general relativistic solutions with a trivial field profile, so the mass and radius are not modified from those in general relativity.

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27

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Black hole perturbations in vector-tensor theories: The odd-mode analysis

Ryotaro Kase, Masato Minamitsuji, Shinji Tsujikawa, Ying-Li Zhang

Journal of Cosmology and Astroparticle Physics 2018 ( 2 ) 1 - 37 2018.02 [Refereed]

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29

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Observational signatures of the parametric amplification of gravitational waves during reheating after inflation

Sachiko Kuroyanagi, Chunshan Lin, Misao Sasaki, Shinji Tsujikawa

Physical Review D 97 ( 2 ) 1 - 18 2018.01 [Refereed]

　View Summary

We study the evolution of gravitational waves (GWs) during and after inflation as well as the resulting observational consequences in a Lorentz-violating massive gravity theory with one scalar (inflaton) and two tensor degrees of freedom. We consider two explicit examples of the tensor mass mg that depends either on the inflaton field φ or on its time derivative φ, both of which lead to parametric excitations of GWs during reheating after inflation. The first example is Starobinsky's R2 inflation model with a φ-dependent mg, and the second is a low energy-scale inflation model with a φ-dependent mg. We compute the energy density spectrum ΩGW(k) today of the GW background. In the Starobinsky's model, we show that the GWs can be amplified up to the detectable ranges of both cosmic microwave background and DECi-hertz Interferometer Gravitational wave Observatory, but the bound from the big bang nucleosynthesis is quite tight to limit the growth. In low-scale inflation with a fast transition to the reheating stage driven by the potential V(φ)=M2φ2/2 around φ≈Mpl (where Mpl is the reduced Planck mass), we find that the peak position of ΩGW(k) induced by the parametric resonance can reach the sensitivity region of advanced LIGO for the Hubble parameter of order 1 GeV at the end of inflation. Thus, our massive gravity scenario offers exciting possibilities for probing the physics of primordial GWs at various different frequencies.

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22

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(Scopus)
Space Gravitational Wave Antenna DECIGO and B-DECIGO

Kawamura, Seiji, Nakamura, Takashi, Ando, Masaki, Seto, Naoki, Akutsu, Tomotada, Funaki, Ikkoh, Ioka, Kunihito, K, a, Nobuyuki, Kawano, Isao, Musha, Mitsuru, Nakazawa, Kazuhiro, Sato, Shuichi, Takashima, Takeshi, Tanaka, Takahiro, Tsubono, Kimio, Yokoyama, Jun'ichi, Agatsuma, Kazuhiro, Aoyanagi, Koh-suke, Arai, Koji, Araya, Akito, Aritomi, Naoki, Asada, Hideki, Aso, Yoichi, Chen, Dan, Chiba, Takeshi, Ebisuzaki, Toshikazu, Eguchi, Satoshi, Ejiri, Yumiko, Enoki, Motohiro, Eriguchi, Yoshiharu, Fujimoto, Masa-Katsu, Fujita, Ryuichi, Fukushima, Mitsuhiro, Futamase, Toshifumi, Gondo, Rina, Harada, Tomohiro, Hashimoto, Tatsuaki, Hayama, Kazuhiro, Hikida, Wataru, Himemoto, Yoshiaki, Hirabayashi, Hisashi, Hiramatsu, Takashi, Hong, Feng-Lei, Horisawa, Hideyuki, Hosokawa, Mizuhiko, Ichiki, Kiyotomo, Ikegami, Takeshi, Inoue, Kaiki T, Ishihara, Hideki, Ishikawa, Takehiko, Ishizaki, Hideharu, Ito, Hiroyuki, Itoh, Yousuke, Izumi, Kiwamu, Kanemura, Shinya, Kawashima, Nobuki, Kawazoe, Fumiko, Kishimoto, Naoko, Kiuchi, Kenta, Kobayashi, Shiho, Kohri, Kazunori, Koizumi, Hiroyuki, Kojima, Yasufumi, Kokeyama, Keiko, Kokuyama, Wataru, Kotake, Kei, Kozai, Yoshihide, Kunimori, Hiroo, Kuninaka, Hitoshi, Kuroda, Kazuaki, Kuroyanagi, Sachiko, Maeda, Kei-ichi, Matsuhara, Hideo, Matsumoto, Nobuyuki, Michimura, Yuta, Miyakawa, Osamu, Miyamoto, Umpei, Miyoki, Shinji, Morimoto, Mutsuko Y, Morisawa, Toshiyuki, Moriwaki, Shigenori, Mukohyama, Shinji, Nagano, Shigeo, Nakamura, Kouji, Nakano, Hiroyuki, Nakao, Kenichi, Nakasuka, Shinichi, Nakayama, Yoshinori, Nishida, Erina, Nishizawa, Atsushi, Niwa, Yoshito, Noumi, Taiga, Obuchi, Yoshiyuki, Ohishi, Naoko, Ohkawa, Masashi, Okada, Kenshi, Okada, Norio, Okutomi, Koki, Oohara, Kenichi, Sago, Norichika, Saijo, Motoyuki, Saito, Ryo, Sakagami, Masaaki, Sakai, Shin-ichiro, Sakata, Shihori, Sasaki, Misao, Sato, Takashi, Shibata, Masaru, Shibata, Kazunori, Shimo-oku, Ayumi, Shinkai, Hisaaki, Shoda, Ayaka, Somiya, Kentaro, Sotani, Hajime, Suemasa, Aru, Sugiyama, Naoshi, Suwa, Yudai, Suzuki, Rieko, Tagoshi, Hideyuki, Takahashi, Fuminobu, Takahashi, Kakeru, Takahashi, Keitaro, Takahashi, Ryutaro, Takahashi, Ryuichi, Takahashi, Hirotaka, Akiteru, Takamori, Takano, Tadashi, Tanaka, Nobuyuki, Taniguchi, Keisuke, Taruya, Atsushi, Tashiro, Hiroyuki, Torii, Yasuo, Toyoshima, Morio, Tsujikawa, Shinji, Ueda, Akitoshi, Ueda, Ken-ichi, Ushiba, Takafumi, Utashima, Masayoshi, Wakabayashi, Yaka, Yagi, Kent, Yamamoto, Kazuhiro, Yamazaki, Toshitaka, Yoo, Chul-Moon, Yoshida, Shijun, Yoshino, Taizoh

International Journal of Modern Physics D 0 ( ja ) 1 - 16 2018 [Refereed]

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87

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Dark energy survivals in massive gravity after GW170817: SO(3) invariant

Lavinia Heisenberg, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2018 ( 1 ) 1 - 35 2018.01 [Refereed]

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15

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(Scopus)
Hairy black-hole solutions in generalized Proca theories

Lavinia Heisenberg, Ryotaro Kase, Masato Minamitsuji, Shinji Tsujikawa

PHYSICAL REVIEW D 96 ( 8 ) 1 - 6 2017.10 [Refereed]

　View Summary

We present a family of exact black-hole solutions on a static spherically symmetric background in second-order generalized Proca theories with derivative vector-field interactions coupled to gravity. We also derive nonexact solutions in power-law coupling models including vector Galileons and numerically show the existence of regular black holes with a primary hair associated with the longitudinal propagation. The intrinsic vector-field derivative interactions generally give rise to a secondary hair induced by nontrivial field profiles. The deviation from General Relativity is most significant around the horizon and hence there is a golden opportunity for probing the Proca hair by the measurements of gravitational waves (GWs) in the regime of strong gravity.

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71

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(Scopus)
Suppression of matter couplings with a vector field in generalized Proca theories

Shintaro Nakamura, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 96 ( 8 ) 1 - 18 2017.10 [Refereed]

　View Summary

In the context of generalized Proca theories, we derive the profile of a vector field A(mu) whose squared A(mu)A(mu) is coupled to the trace T of matter on a static and spherically symmetric background. The cubic Galileon self-interaction leads to the suppression of a longitudinal vector component due to the operation of the Vainshtein mechanism. For quartic and sixth-order derivative interactions, the solutions consistent with those in the continuous limit of small derivative couplings correspond to the branch with the vanishing longitudinal mode. We compute the corrections to gravitational potentials outside a compact body induced by the vector field in the presence of cubic, quartic, and sixth-order derivative couplings, and show that the models can be consistent with local gravity constraints under mild bounds on the temporal vector component. The quintic vector Galileon does not allow regular solutions of the longitudinal mode for a rapidly decreasing matter density outside the body.

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17

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Black holes in vector-tensor theories

Lavinia Heisenberg, Ryotaro Kase, Masato Minamitsuji, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 1708 ( 8 ) 1 - 38 2017.08 [Refereed]

　View Summary

We study static and spherically symmetric black hole (BH) solutions in second-order generalized Proca theories with nonminimal vector field derivative couplings to the Ricci scalar, the Einstein tensor, and the double dual Riemann tensor. We find concrete Lagrangians which give rise to exact BH solutions by imposing two conditions of the two identical metric components and the constant norm of the vector field. These exact solutions are described by either Reissner-Nordstrom (RN), stealth Schwarzschild, or extremal RN solutions with a non-trivial longitudinal mode of the vector field. We then numerically construct BH solutions without imposing these conditions. For cubic and quartic Lagrangians with power-law couplings which encompass vector Galileons as the specific cases, we show the existence of BH solutions with the difference between two non-trivial metric components. The quintic-order power-law couplings do not give rise to non-trivial BH solutions regular throughout the horizon exterior. The sixth-order and intrinsic vector-mode couplings can lead to BH solutions with a secondary hair. For all the solutions, the vector field is regular at least at the future or past horizon. The deviation from General Relativity induced by the Proca hair can be potentially tested by future measurements of gravitational waves in the nonlinear regime of gravity.

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73

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The status of DECIGO

Shuichi Sato, Seiji Kawamura, Masaki Ando, Takashi Nakamura, Kimio Tsubono, Akito Araya, Ikkoh Funaki, Kunihito Ioka, Nobuyuki Kanda, Shigenori Moriwaki, Mitsuru Musha, Kazuhiro Nakazawa, Kenji Numata, Shin Ichiro Sakai, Naoki Seto, Takeshi Takashima, Takahiro Tanaka, Kazuhiro Agatsuma, Koh Suke Aoyanagi, Koji Arai, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei Ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shinji Mukohyama, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Norio Okada, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shihori Sakata, Misao Sasaki

Journal of Physics: Conference Series 840 ( 1 ) 1 - 8 2017.06 [Refereed]

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188

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Observational constraints on generalized Proca theories

Antonio De Felice, Lavinia Heisenberg, Shinji Tsujikawa

PHYSICAL REVIEW D 95 ( 12 ) 1 - 18 2017.06 [Refereed]

　View Summary

In a model of the late-time cosmic acceleration within the framework of generalized Proca theories, there exists a de Sitter attractor preceded by the dark energy equation of state w(DE) = -1 -s, where s is a positive constant. We run the Markov-chain-Monte Carlo code to confront the model with the observational data of the cosmic microwave background (CMB), baryon acoustic oscillations, supernovae type Ia, and local measurements of the Hubble expansion rate for the background cosmological solutions and obtain the bound s = 0.254(-0.097)(+0.118) at 95% confidence level (C.L.). Existence of the additional parameter s to those in the Lambda-cold-dark-matter (Lambda CDM) model allows to reduce tensions of the Hubble constant H-0 between the CMB and the low-redshift measurements. Including the cosmic growth data of redshift-space distortions in the galaxy power spectrum and taking into account no-ghost and stability conditions of cosmological perturbations, we find that the bound on s is shifted to s = 0.16(-0.08)(+0.08) (95% C.L.) and hence the model with s > 0 is still favored over Lambda CDM model. Apart from the quantities s, H-0 and the today's matter density parameter Omega(m0), the constraints on other model parameters associated with perturbations are less stringent, reflecting the fact that there are different sets of parameters that give rise to a similar cosmic expansion and growth history.

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63

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Cosmology in beyond-generalized Proca theories

Shintaro Nakamura, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 95 ( 10 ) 1 - 22 2017.05 [Refereed]

　View Summary

The beyond-generalized Proca theories are the extension of second-order massive vector-tensor theories (dubbed generalized Proca theories) with two transverse vector modes and one longitudinal scalar besides two tensor polarizations. Even with this extension, the propagating degrees of freedom remain unchanged on the isotropic cosmological background without an Ostrogradski instability. We study the cosmology in beyond-generalized Proca theories by paying particular attention to the dynamics of late-time cosmic acceleration and resulting observational consequences. We derive conditions for avoiding ghosts and instabilities of tensor, vector, and scalar perturbations and discuss viable parameter spaces in concrete models allowing the dark energy equation of state smaller than -1. The propagation speeds of those perturbations are subject to modifications beyond the domain of generalized Proca theories. There is a mixing between scalar and matter sound speeds, but such a mixing is suppressed during most of the cosmic expansion history without causing a new instability. On the other hand, we find that derivative interactions arising in beyond-generalized Proca theories give rise to important modifications to the cosmic growth history. The growth rate of matter perturbations can be compatible with the redshift-space distortion data due to the realization of gravitational interaction weaker than that in generalized Proca theories. Thus, it is possible to distinguish the dark energy model in beyond-generalized Proca theories from the counterpart in generalized Proca theories as well as from the Lambda CDM model.

DOI
Instabilities in Horndeski-Yang-Mills inflation

Jose Beltran Jimenez, Lavinia Heisenberg, Ryotaro Kase, Ryo Namba, Shinji Tsujikawa

PHYSICAL REVIEW D 95 ( 6 ) 1 - 8 2017.03 [Refereed]

　View Summary

A non-Abelian SU(2) gauge field with a nonminimal Horndeski coupling to gravity gives rise to a de Sitter solution followed by a graceful exit to a radiation-dominated epoch. In this Horndeski-Yang-Mills (HYM) theory we derive the second-order action for tensor perturbations on the homogeneous and isotropic quasi-de Sitter background. We find that the presence of the Horndeski nonminimal coupling to the gauge field inevitably introduces ghost instabilities in the tensor sector during inflation. Moreover, we also find Laplacian instabilities for the tensor perturbations deep inside the Hubble radius during inflation. Thus, we conclude that the HYM theory does not provide a consistent inflationary framework due to the presence of ghosts and Laplacian instabilities.

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16

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Absence of solid angle deficit singularities in beyond-generalized proca theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 94 ( 12 ) 1 - 14 2016.12 [Refereed]

　View Summary

In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) scalar-tensor theories, which are outside the domain of second-order Horndeski theories, it is known that there exists a solid angle deficit singularity in the case where the parameter alpha(H) characterizing the deviation from Horndeski theories approaches a nonvanishing constant at the center of a spherically symmetric body. Meanwhile, it was recently shown that second-order generalized Proca theories with a massive vector field A(mu) can be consistently extended to beyond-generalized Proca theories, which recover shift-symmetric GLPV theories in the scalar limit A(mu) -> del(mu)chi In beyond-generalized Proca theories up to quartic-order Lagrangians, we show that solid angle deficit singularities are generally absent due to the existence of a temporal vector component. We also derive the vector-field profiles around a compact object and show that the success of the Vainshtein mechanism operated by vector Galileons is not prevented by new interactions in beyond generalized Proca theories.

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9

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Anisotropic cosmological solutions in massive vector theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 1611 ( 11 ) 1 - 28 2016.11 [Refereed]

　View Summary

In beyond-generalized Proca theories including the extension to theories higher than second order, we study the role of a spatial component v of a massive vector field on the anisotropic cosmological background. We show that, as in the case of the isotropic cosmological background, there is no additional ghostly degrees of freedom associated with the Ostrogradski instability. In second-order generalized Proca theories we find the existence of anisotropic solutions on which the ratio between the anisotropic expansion rate Sigma and the isotropic expansion rate H remains nearly constant in the radiation-dominated epoch. In the regime where Sigma/H is constant, the spatial vector component v works as a dark radiation with the equation of state close to 1/3. During the matter era, the ratio Sigma/H decreases with the decrease of v. As long as the conditions |Sigma| << H and v (2 <<) phi(2) are satisfied around the onset of late-time cosmic acceleration, where phi is the temporal vector component, we find that the solutions approach the isotropic de Sitter fixed point ( Sigma = 0 = v) in accordance with the cosmic no-hair conjecture. In the presence of v and Sigma the early evolution of the dark energy equation of state wDE in the radiation era is different from that in the isotropic case, but the approach to the isotropic value w(DE)((iso)) typically occurs at redshifts z much larger than 1. Thus, apart from the existence of dark radiation, the anisotropic cosmological dynamics at low redshifts is similar to that in isotropic generalized Proca theories. In beyond-generalized Proca theories the only consistent solution to avoid the divergence of a determinant of the dynamical system corresponds to v = 0, so Sigma always decreases in time.

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42

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Beyond generalized Proca theories

Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa

PHYSICS LETTERS B 760 617 - 626 2016.09 [Refereed]

　View Summary

We consider higher-order derivative interactions beyond second-order generalized Proca theories that propagate only the three desired polarizations of a massive vector field besides the two tensor polarizations from gravity. These new interactions follow the similar construction criteria to those arising in the extension of scalar-tensor Horndeski theories to Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories. On the isotropic cosmological background, we show the existence of a constraint with a vanishing Hamiltonian that removes the would-be Ostrogradski ghost. We study the behavior of linear perturbations on top of the isotropic cosmological background in the presence of a matter perfect fluid and find the same number of propagating degrees of freedom as in generalized Proca theories (two tensor polarizations, two transverse vector modes, and two scalar modes). Moreover, we obtain the conditions for the avoidance of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations. We observe key differences in the scalar sound speed, which is mixed with the matter sound speed outside the domain of generalized Proca theories. (C) 2016 The Authors. Published by Elsevier B.V.

DOI

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122

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Cosmic microwave background and inflation in multi-fractional spacetimes

Gianluca Calcagni, Sachiko Kuroyanagi, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 08 ( 8 ) 1 - 32 2016.08 [Refereed]

　View Summary

We use FIRAS and PLANCK 2015 data to place observational bounds on inflationary in multi-fractional spacetimes with q-derivatives. While a power-law expansion in the geometric time coordinate is subject to the usual constraints from the tensor-to-scalar ratio, model-independent best fits of the black-body and scalar spectra yield upper limits on the free parameters of the multi-fractal measure of the theory. When the measure describing the fractal spacetime geometry is non-oscillating, information on the CMB black-body spectrum places constraints on the theory independent from but weaker than those obtained from the Standard Model, astrophysical gravitational waves and gamma-ray bursts (GRBS). When log oscillations are included and the measure describes a discrete fractal spacetime at microscopic scales, we obtain the first observational constraints on the amplitudes of such oscillations and find, in general, strong constraints on the multi-scale geometry and on the dimension of space. These results complete the scan and reduction of the parameter space of the theory. Black-body bounds are obtained also for the theory with weighted derivatives.

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31

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Effective gravitational couplings for cosmological perturbations in generalized Proca theories

Antonio De Felice, Lavinia Heisenberg, Ryotaro Kase, Shinji Mukohyama, Shinji Tsujikawa, Ying-li Zhang

PHYSICAL REVIEW D 94 ( 4 ) 1 - 20 2016.08 [Refereed]

　View Summary

We consider the finite interactions of the generalized Proca theory including the sixth-order Lagrangian and derive the full linear perturbation equations of motion on the flat Friedmann-Lemaltre-RobertsonWalker background in the presence of a matter perfect fluid. By construction, the propagating degrees of freedom (besides the matter perfect fluid) are two transverse vector perturbations, one longitudinal scalar, and two tensor polarizations. The Lagrangians associated with intrinsic vector modes neither affect the background equations of motion nor the second-order action of tensor perturbations, but they do give rise to nontrivial modifications to the no-ghost condition of vector perturbations and to the propagation speeds of vector and scalar perturbations. We derive the effective gravitational coupling G(eff) with matter density perturbations under a quasistatic approximation on scales deep inside the sound horizon. Wc find that the existence of intrinsic vector modes allows a possibility for reducing G(eff). in fact, within the parameter space, G(eff) can be even smaller than the Newton gravitational constant G at the late cosmological epoch, with a peculiar phantom dark energy equation of state (without ghosts). The modifications to the slip parameter eta and the evolution of the growth rate f sigma(8) are discussed as well. Thus, dark energy models in the framework of generalized Proca theories can be observationally distinguished from the ACDM model according to both cosmic growth and expansion history. Furthermore, we study the evolution of vector perturbations and show that outside the vector sound horizon the perturbations are nearly frozen and start to decay with oscillations after the horizon entry.

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114

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Cosmology in generalized Proca theories

Antonio De Felice, Lavinia Heisenberg, Ryotaro Kase, Shinji Mukohyama, Shinji Tsujikawa, Ying-li Zhang

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 06 ( 6 ) 1 - 33 2016.06 [Refereed]

　View Summary

We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable parameter spaces in which the no-ghost and stability conditions are satisfied during the cosmic expansion history.

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145

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The Subaru FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at z similar to 1.4

Teppei Okumura, Chiaki Hikage, Tomonori Totani, Motonari Tonegawa, Hiroyuki Okada, Karl Glazebrook, Chris Blake, Pedro G. Ferreira, Surhud More, Atsushi Taruya, Shinji Tsujikawa, Masayuki Akiyama, Gavin Dalton, Tomotsugu Goto, Takashi Ishikawa, Fumihide Iwamuro, Takahiko Matsubara, Takahiro Nishimichi, Kouji Ohta, Ikkoh Shimizu, Ryuichi Takahashi, Naruhisa Takato, Naoyuki Tamura, Kiyoto Yabe, Naoki Yoshida

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 68 ( 3 ) 1 - 24 2016.06 [Refereed]

　View Summary

We measure the redshift-space correlation function from a spectroscopic sample of 2783 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers a redshift range of 1.19 < z < 1.55, is the first cosmological study at such high redshifts. We detect clear anisotropy due to redshift-space distortions (RSD) both in the correlation function as a function of separations parallel and perpendicular to the line of sight and its quadrupole moment. RSD has been extensively used to test general relativity on cosmological scales at z < 1. Adopting a Lambda CDM cosmology with the fixed expansion history and no velocity dispersion (sigma(v) = 0), and using the RSD measurements on scales above 8 h(-1) Mpc, we obtain the first constraint on the growth rate at the redshift, f(z)sigma(8)(z) = 0.482 +/- 0.116 at z similar to 1.4 after marginalizing over the galaxy bias parameter b(z)sigma(8)(z). This corresponds to 4.2 sigma detection of RSD. Our constraint is consistent with the prediction of general relativity f sigma(8) similar to 0.392 within the 1 sigma confidence level. When we allow sv to vary and marginalize over it, the growth rate constraint becomes f sigma(8) = 0.494(-0.120)(+0.126). We also demonstrate that by combining with the low-z constraints on f sigma(8), high-z galaxy surveys like the FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.

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192

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Screening fifth forces in generalized Proca theories

Antonio De Felice, Lavinia Heisenberg, Ryotaro Kase, Shinji Tsujikawa, Ying-li Zhang, Gong-Bo Zhao

PHYSICAL REVIEW D 93 ( 10 ) 1 - 17 2016.05 [Refereed]

　View Summary

For a massive vector field with derivative self-interactions, the breaking of the gauge invariance allows the propagation of a longitudinal mode in addition to the two transverse modes. We consider generalized Proca theories with second-order equations of motion in a curved space-time and study how the longitudinal scalar mode of the vector field gravitates on a spherically symmetric background. We show explicitly that cubic-order self-interactions lead to the suppression of the longitudinal mode through the Vainshtein mechanism. Provided that the dimensionless coupling of the interaction is not negligible, this screening mechanism is sufficiently efficient to give rise to tiny corrections to gravitational potentials consistent with solar-system tests of gravity. We also study the quartic interactions with the presence of nonminimal derivative coupling with the Ricci scalar and find the existence of solutions where the longitudinal mode completely vanishes. Finally, we discuss the case in which the effect of the quartic interactions dominates over the cubic one and show that local gravity constraints can be satisfied under a mild bound on the parameters of the theory.

DOI

Scopus

78

Citation

(Scopus)
Conical singularities and the Vainshtein screening in full GLPV theories

Ryotaro Kase, Shinji Tsujikawa, Antonio De Felice

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 03 ( 3 ) 1 - 25 2016.03 [Refereed]

　View Summary

In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, it is known that the conical singularity arises at the center of a spherically symmetric body (r = 0) in the case where the parameter alpha(H4) characterizing the deviation from the Horndeski Lagrangian L-4 approaches a non-zero constant as r -> 0. We derive spherically symmetric solutions around the center in full GLPV theories and show that the GLPV Lagrangian does not modify the divergent property of the Ricci scalar R induced by the non-zero alpha(H4). Provided that alpha(H4) = 0, curvature scalar quantities can remain finite at r = 0 even in the presence of L-5 beyond the Horndeski domain. For the theories in which the scalar field phi is directly coupled to R we also obtain spherically symmetric solutions inside/outside the body to study whether the fifth force mediated by phi can be screened by non-linear field self-interactions. We find that there is one specific model of GLPV theories in which the effect of L5 vanishes in the equations of motion. We also show that, depending on the sign of a L-5-dependent term in the field equation, the model can be compatible with solar-system constraints under the Vainshtein mechanism or it is plagued by the problem of a divergence of the field derivative in high-density regions.

DOI

Scopus

13

Citation

(Scopus)
Cosmology with a successful Vainshtein screening in theories beyond Horndeski

Ryotaro Kase, Shinji Tsujikawa, Antonio De Felice

PHYSICAL REVIEW D 93 ( 2 ) 1 - 17 2016.01 [Refereed]

　View Summary

We propose a dark energy model where a scalar field phi has nonlinear self-interactions in the presence of a dilatonic coupling with the Ricci scalar. This belongs to a subclass of theories beyond Horndeski, which accommodates covariant Galileons and Brans-Dicke theories as specific cases. We derive conditions under which the scalar sound speed squared c(s)(2) is positive from the radiation era to today. Since c(s)(2) remains smaller than the order of 1, the deviation from Horndeski theories does not cause heavy oscillations of gaugeinvariant gravitational potentials. In this case, the evolution of matter perturbations at low redshifts is similar to that in the coupled dark energy scenario with an enhanced gravitational interaction. On the spherically symmetric background with a matter source, the existence of field self-interactions suppresses the propagation of the fifth force inside a Vainshtein radius. We estimate an allowed parameter space in which the model can be compatible with Solar System constraints while satisfying conditions for the cosmological viability of background and perturbations.

DOI

Scopus

23

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(Scopus)
Existence and disappearance of conical singularities in Gleyzes-Langlois-Piazza-Vernizzi theories

Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 92 ( 12 ) 1 - 11 2015.12 [Refereed]

　View Summary

In a class of Gleyzes-Langlois-Piazza-Vernizzi theories, we derive both vacuum and interior Schwarzs-child solutions under the condition that the derivatives of a scalar field phi with respect to the radius r vanish. If the parameter alpha(H) characterizing the deviation from Horndeski theories approaches a nonzero constant at the center of a spherically symmetric body, we find that the conical singularity arises at r = 0 with the Ricci scalar given by R = -2 alpha(H)/r(2). This originates from violation of the geometrical structure of four-dimensional curvature quantities. The conical singularity can disappear for the models in which the parameter alpha(H) vanishes in the limit that r -> 0. We propose explicit models without the conical singularity by properly designing the classical Lagrangian in such a way that the main contribution to alpha(H) comes from the field derivative phi'(r) around r = 0. We show that the extension of covariant Galileons with a diatonic coupling allows for the recovery of general relativistic behavior inside a so-called Vainshtein radius. In this case, both the propagation of a fifth force and the deviation from Horndeski theories are suppressed outside a compact body in such a way that the model is compatible with local gravity experiments inside the solar system.

DOI

Scopus

16

Citation

(Scopus)
曲がった時空のミステリー: ダークエネルギーと重力理論の変更

辻川信二

数理科学 53 ( 2015年12月 ) 27 - 33 2015.12 [Invited]

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Cosmological disformal transformations to the Einstein frame and gravitational couplings with matter perturbations

Shinji Tsujikawa

PHYSICAL REVIEW D 92 ( 6 ) 1 - 23 2015.09 [Refereed]

　View Summary

The disformal transformation of metric g(mu nu) -> Omega(2) (phi)g(mu nu) + Gamma(phi, X)partial derivative(mu)phi partial derivative(nu)phi, where phi is a scalar field with the kinetic energy X = partial derivative(mu)phi partial derivative(mu)phi/2, preserves the Lagrangian structure of Gleyzes-Langlois-Piazza-Vernizzi theories (which is the minimum extension of Horndeski theories). In the presence of matter, this transformation gives rise to a kinetic-type coupling between the scalar field phi and matter. We consider the Einstein frame in which the second-order action of tensor perturbations on the isotropic cosmological background is of the same form as that in General Relativity and study the role of couplings at the levels of both background and linear perturbations. We show that the effective gravitational potential felt by matter perturbations in the Einstein frame can be conveniently expressed in terms of the sum of a General Relativistic contribution and couplings induced by the modification of gravity. For the theories in which the transformed action belongs to a class of Horndeski theories, there is no anisotropic stress between two gravitational potentials in the Einstein frame due to a gravitational demixing. We propose a concrete dark energy model encompassing Brans-Dicke theories as well as theories with the tensor propagation speed c(t) different from 1. We clarify the correspondence between physical quantities in the Jordan/Einstein frames and study the evolution of gravitational potentials and matter perturbations from the matter-dominated epoch to today in both analytic and numerical approaches.

DOI

Scopus

20

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(Scopus)
Possibility of realizing weak gravity in redshift space distortion measurements

Shinji Tsujikawa

PHYSICAL REVIEW D 92 ( 4 ) 1 - 16 2015.08 [Refereed]

　View Summary

We study the possibility of realizing a growth rate of matter density perturbations lower than that in general relativity. Using the approach of the effective field theory of modified gravity encompassing theories beyond Horndeski, we derive the effective gravitational coupling G(eff) and the gravitational slip parameter eta for perturbations deep inside the Hubble radius. In Horndeski theories we derive a necessary condition for achieving weak gravity associated with tensor perturbations, but this is not a sufficient condition due to the presence of a scalar-matter interaction that always enhances G(eff). Beyond the Horndeski domain it is possible to realize G(eff) smaller than Newton's gravitational constant G, while the scalar and tensor perturbations satisfy no-ghost and stability conditions. We present a concrete dark energy scenario with varying c(t) and numerically study the evolution of perturbations to confront the model with the observations of redshift-space distortions and weak lensing.

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42

Citation

(Scopus)
Planck constraints on inflation in auxiliary vector modified f(R) theories

Mehmet Ozkan, Yi Pang, Shinji Tsujikawa

PHYSICAL REVIEW D 92 ( 2 ) 1 - 10 2015.07 [Refereed]

　View Summary

We show that the universal alpha-attractor models of inflation can be realized by including an auxiliary vector field A(mu) for the Starobinsky model with the Lagrangian f(R) = R + R-2/(6M(2)). If the same procedure is applied to general modified f(R) theories in which the Ricci scalar R is replaced by R + A(mu)A(mu) + beta del(mu)A(mu) with constant beta, we obtain the Brans-Dicke theory with a scalar potential and the BransDicke parameter omega(BD) = beta(2)/4. We also place observational constraints on inflationary models based on auxiliary vector modified f(R) theories from the latest Planck measurements of the cosmic microwave background anisotropies in both temperature and polarization. In the modified Starobinsky model, we find that the parameter beta is constrained to be beta < 25 (68% confidence level) from the bounds of the scalar spectral index and the tensor-to-scalar ratio.

DOI

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12

Citation

(Scopus)
Inflationary gravitational waves in the effective field theory of modified gravity

Antonio De Felice, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 91 ( 10 ) 2015.05 [Refereed]

DOI

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19

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(Scopus)
Observational signatures of the theories beyond Horndeski

Antonio De Felice, Kazuya Koyama, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 05 ( 5 ) 1 - 27 2015.05 [Refereed]

　View Summary

In the approach of the effective field theory of modified gravity, we derive the equations of motion for linear perturbations in the presence of a barotropic perfect fluid on the flat isotropic cosmological background. In a simple version of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, which is the minimum extension of Horndeski theories, we show that a slight deviation of the tensor propagation speed squared c(t)(2) from 1 generally leads to the large modification to the propagation speed squared c(s)(2) of a scalar degree of freedom phi. This problem persists whenever the kinetic energy rho(X) of the field phi is much smaller than the background energy density rho(m), which is the case for most of dark energy models in the asymptotic past. Since the scaling solution characterized by the constant ratio rho(X)/rho(m) is one way out for avoiding such a problem, we study the evolution of perturbations for a scaling dark energy model in the framework of GLPV theories in the Jordan frame. Provided the oscillating mode of scalar perturbations is fine-tuned so that it is initially suppressed, the anisotropic parameter eta = -Phi/Psi between the two gravitational potentials Psi and Phi significantly deviates from 1 for c(t)(2) away from 1. For other general initial conditions, the deviation of c(t)(2) from 1 gives rise to the large oscillation of Psi with the frequency related to c(s)(2). In both cases, the model can leave distinct imprints for the observations of CMB and weak lensing.

DOI

Scopus

31

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(Scopus)
Inflationary gravitational waves in the effective field theory of modified gravity

Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 91 ( 10 ) 1 - 11 2015.05 [Refereed]

　View Summary

In the approach of the effective field theory of modified gravity, we derive the second-order action and the equation of motion for tensor perturbations on the flat isotropic cosmological background. This analysis accommodates a wide range of gravitational theories including Horndeski theories, its generalization, and the theories with spatial derivatives higher than second order (e.g., Horava-Lifshitz gravity). We obtain the inflationary power spectrum of tensor modes by taking into account corrections induced by higher-order spatial derivatives and slow-roll corrections to the de Sitter background. We also show that the leading-order spectrum in concrete modified gravitational theories can be mapped on to that in General Relativity under a disformal transformation. Our general formula will be useful to constrain inflationary models from the future precise measurement of the B-mode polarization in the cosmic microwave background.

DOI

Scopus

19

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(Scopus)
Disformal invariance of cosmological perturbations in a generalized class of Horndeski theories

Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 04 ( 4 ) 1 - 26 2015.04 [Refereed]

　View Summary

It is known that Horndeski theories can be transformed to a,sub-class of Gleyzes-Langlois-Piazza-Vernizzi (MTV) theories under the disformal transformation of the metric g(mu v) -> Omega(2)(phi)g(mu v) + Gamma(phi, X)del(mu)phi del(v)phi, where Omega is a function of a scalar field phi and Gamma is another function depending on both phi and X - g(mu v)del(mu)phi del(v)phi. We show that, with the choice of unitary gauge, both curvature and tensor perturbations on the Hat isotropic cosmological background are generally invariant under the disformal transformation. By means of the effective field theories (mcompassing florndeski and GLPV theories, we obtain the secondorder actions of scalar/tensor perturbations and present the relations for physical quantities betAveen the two frames. The invariance of the inflationary power spectra under the disformal transformation is explicitly proved up to next-to-leading order in slow-roll. In particular, we identify the existence of the Einstein frame in which the tensor power spectrum is of the same form as that in General Relativity and derive the condition under which the spectrum of gravitational waves in GLPV theories is red-tilted.

DOI

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46

Citation

(Scopus)
Vainshtein mechanism with a generalized Galileon term

Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

The 13th Marcel Grossmann Meeting: On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories - Proceedings of the MG13 Meeting on General Relativity, 2012 The Thirteenth Marcel Grossman ( 210699 ) 1304 - 1306 2015

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The viability of potential-driven galileon inflation

Junko Ohashi, Shinji Tsujikawa

The 13th Marcel Grossmann Meeting: On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories - Proceedings of the MG13 Meeting on General Relativity, 2012 Marcel Grossmann Meeting ( 210699 ) 1522 - 1524 2015

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Discrimination between dark energy models from recent observations

Shinji Tsujikawa

The 13th Marcel Grossmann Meeting: On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories - Proceedings of the MG13 Meeting on General Relativity, 2012 The Thirteenth Marcel Grossman ( 210699 ) 1531 - 1533 2015

DOI

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Effective field theory of modified gravity on the spherically symmetric background: Leading order dynamics and the odd-type perturbations

Ryotaro Kase, László Á. Gergely, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 90 ( 12 ) 2014.12 [Refereed]

DOI

Scopus

33

Citation

(Scopus)
Effective field theory of modified gravity on the spherically symmetric background: Leading order dynamics and the odd-type perturbations

Ryotaro Kase, Laszlo A. Gergely, Shinji Tsujikawa

PHYSICAL REVIEW D 90 ( 12 ) 1 - 21 2014.12 [Refereed]

　View Summary

We consider perturbations of a static and spherically symmetric background endowed with a metric tensor and a scalar field in the framework of the effective field theory of modified gravity. We employ the previously developed 2 + 1 + 1 canonical formalism of a double Arnowitt-Deser-Misner (ADM) decomposition of space-time, which singles out both time and radial directions. Our building block is a general gravitational action that depends on scalar quantities constructed from the 2 + 1 + 1 canonical variables and the lapse. Variation of the action up to first order in perturbations gives rise to three independent background equations of motion, as expected from spherical symmetry. The dynamical equations of linear perturbations follow from the second-order Lagrangian after a suitable gauge fixing. We derive conditions for the avoidance of ghosts and Laplacian instabilities for the odd-type perturbations. We show that our results not only incorporate those derived in the most general scalar-tensor theories with second-order equations of motion (the Horndeski theories) but they can be applied to more generic theories beyond Horndeski.

DOI

Scopus

33

Citation

(Scopus)
Effective field theory approach to modified gravity including Horndeski theory and Horava-Lifshitz gravity

Ryotaro Kase, Shinji Tsujikawa

INTERNATIONAL JOURNAL OF MODERN PHYSICS D 23 ( 13 ) 1 - 41 2014.11 [Refereed] [Invited]

DOI

Scopus

60

Citation

(Scopus)
Implications of the B-mode polarization measurement for direct detection of inflationary gravitational waves

Sachiko Kuroyanagi, Shinji Tsujikawa, Takeshi Chiba, Naoshi Sugiyama

PHYSICAL REVIEW D 90 ( 6 ) 1 - 14 2014.09 [Refereed]

　View Summary

The prospects for direct measurements of inflationary gravitational waves by next generation interferometric detectors inferred from the possible detection of B-mode polarization of the cosmic microwave background are studied. We compute the spectra of the gravitational wave background and the signal-to-noise ratios by two interferometric detectors (DECIGO and BBO) for large-field inflationary models in which the tensor-to-scalar ratio is greater than the order of 0.01. If the reheating temperature T-RH of chaotic inflation with the quadratic potential is high (T-RH > 7.9 x 10(6) GeV for upgraded DECIGO and T-RH > 1.8 x 10(6) GeV for BBO), it will be possible to reach the sensitivity of the gravitational background in future experiments at 3 sigma confidence level. The direct detection is also possible for natural inflation with the potential V(phi) = A(4) [1 - cos(phi/f)], provided that f > 4.2M(pl) (upgraded DECIGO) and f > 3.6M(pl) (BBO) with T-RH higher than 10(8) GeV. The quartic potential V(phi) = lambda phi(4)/4 with a nonminimal coupling xi between the inflaton field phi and the Ricci scalar R gives rise to a detectable level of gravitational waves vertical bar xi vertical bar for smaller than the order of 0.01, irrespective of the reheating temperature.

DOI

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33

Citation

(Scopus)
Cosmology in generalized Horndeski theories with second-order equations of motion

Ryotaro Kase, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 90 ( 4 ) 2014.08 [Refereed]

DOI

Scopus

51

Citation

(Scopus)
Cosmology in generalized Horndeski theories with second-order equations of motion

Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 90 ( 4 ) 1 - 15 2014.08 [Refereed]

　View Summary

We study the cosmology of an extended version of Horndeski theories with second-order equations of motion on the flat Friedmann-Lemaitre-Robertson-Walker background. In addition to a dark energy field chi associated with the gravitational sector, we take into account multiple scalar fields phi(I) (I = 1, 2, ... , N - 1) characterized by the Lagrangians P-(I) (X-I) with X-I = partial derivative(mu)phi(I)partial derivative(mu)phi(I). These additional scalar fields can model the perfect fluids of radiation and nonrelativistic matter. We derive propagation speeds of scalar and tensor perturbations as well as conditions for the absence of ghosts. The theories beyond Horndeski induce nontrivial modifications to all the propagation speeds of N scalar fields, but the modifications to those for the matter fields phi(I) are generally suppressed relative to that for the dark energy field chi. We apply our results to the covariantized Galileon with an Einstein-Hilbert term in which partial derivatives of the Minkowski Galileon are replaced by covariant derivatives. Unlike the covariant Galileon with second-order equations of motion in general space-time, the scalar propagation speed square c(s1)(2) associated with the field chi becomes negative during the matter era for late-time tracking solutions, so the two Galileon theories can be clearly distinguished at the level of linear cosmological perturbations.

DOI

Scopus

51

Citation

(Scopus)
Dark Energy and Modified Gravity

Tsujikawa Shinji

69 ( 7 ) 444 - 452 2014.07 [Refereed] [Invited]

　View Summary

The observational evidence of dark energy is one of the most serious problems in modern cosmology. From the joint constraints on the dark energy equation of state using the recent data of SN Ia, CMB and BAO, there is a possibility that the gravitational law may be modified from General Relativity at large distances. We review a number of theoretical models of modified gravity which can account for the cosmic acceleration, while recovering the General Relativistic behavior in the solar system. We also discuss the growth of structures in modified gravity models in order to confront them with the observations of galaxy clusterings and weak lensing.

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Cosmological perturbations and observational constraints on nonlocal massive gravity

Savvas Nesseris, Shinji Tsujikawa

PHYSICAL REVIEW D 90 ( 2 ) 1 - 13 2014.07 [Refereed]

　View Summary

Nonlocal massive gravity can provide an interesting explanation for the late-time cosmic acceleration, with a dark energy equation of state w(DE) smaller than -1 in the past. We derive the equations of linear cosmological perturbations to confront such models with the observations of large-scale structures. The effective gravitational coupling to nonrelativistic matter associated with galaxy clusterings is close to Newton's gravitational constant G for a mass scale m slightly smaller than today's Hubble parameter H-0. Taking into account the background expansion history as well as the evolution of matter perturbations delta(m), we test for these models with Type Ia Supernovae (SnIa) from Union 2.1, the cosmic microwave background (CMB) measurements from Planck, a collection of baryon acoustic oscillations (BAO), and the growth rate data of delta(m). Using a higher value of H-0 derived from its direct measurement (H-0 greater than or similar to 70 km s(-1) Mpc(-1)) the data strongly support the nonlocal massive gravity model (-1.1 less than or similar to w(DE) less than or similar to -1.04 in the past) over the ACDM model (w(DE) = -1), whereas for a lower prior (67 km s(-1) Mpc(-1) less than or similar to H-0 less than or similar to 70 km s(-1) Mpc(-1)) the two models are statistically comparable.

DOI

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38

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Cosmological scaling solutions for multiple scalar fields

Takeshi Chiba, Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 90 ( 2 ) 1 - 19 2014.07 [Refereed]

　View Summary

The general k-essence Lagrangian for the existence of cosmological scaling solutions is derived in the presence of multiple scalar fields coupled to a barotropic perfect fluid. In addition to the scaling fixed point associated with the dynamics during the radiation and matter eras, we also obtain a scalar-field dominated solution relevant to dark energy and discuss the stability of them in the two-field setup. We apply our general results to a model of two canonical fields with coupled exponential potentials arising in string theory. Depending on model parameters and initial conditions, we show that the scaling matter-dominated epochs followed by an attractor with cosmic acceleration can be realized with/without the couplings to scalar fields. The different types of scaling solutions can be distinguished from each other by the evolution of the dark energy equation of state from high redshifts to today.

DOI

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17

Citation

(Scopus)
Distinguishing between inflationary models from cosmic microwave background

Shinji Tsujikawa

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS 06 ( 6 ) 1 - 26 2014.06 [Refereed] [Invited]

DOI

Scopus

16

Citation

(Scopus)
Strong Planck constraints on braneworld and non-commutative inflation

Gianluca Calcagni, Sachiko Kuroyanagi, Junko Ohashi, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 03 ( 3 ) 1 - 23 2014.03 [Refereed]

　View Summary

We place observational likelihood constraints on braneworld and non-commutative inflation for a number of inflaton potentials, using Planck, WMAP polarization and BAO data. Both braneworld and non-commutative scenarios of the kind considered here are limited by the most recent data even more severely than standard general-relativity models. At more than 95% confidence level, the monomial potential V (phi) proportional to phi(p) is ruled out for p >= 2 in the Randall-Sundrum (RS) braneworld cosmology and, for p > 0, also in the high-curvature limit of the Gauss-Bonnet (GB) braneworld and in the infrared limit of non-commutative inflation, due to a large scalar spectral index. Some parameter values for natural inflation, small-varying inflaton models and Starobinsky inflation are allowed in all scenarios, although some tuning is required for natural inflation in a non-commutative spacetime.

DOI

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34

Citation

(Scopus)
Effective field theory of modified gravity with two scalar fields: Dark energy and dark matter

Laszlo A. Gergely, Shinji Tsujikawa

PHYSICAL REVIEW D 89 ( 6 ) 1 - 18 2014.03 [Refereed]

　View Summary

We present a framework for discussing the cosmology of dark energy and dark matter based on two scalar degrees of freedom. An effective field theory of cosmological perturbations is employed. A unitary gauge choice renders the dark energy field into the gravitational sector, for which we adopt a generic Lagrangian depending on three- dimensional geometrical scalar quantities arising in the Arnowitt- DeserMisner decomposition. We add to this dark energy- associated gravitational sector a scalar field. and its kinetic energy X as dark matter variables. Compared to the single- field case, we find that there are additional conditions to obey in order to keep the equations of motion for linear cosmological perturbations at second order. For such a second- order multifield theory, we derive conditions under which ghosts and Laplacian instabilities of the scalar and tensor perturbations are absent. We apply our general results to models with dark energy emerging in the framework of the Horndeski theory and dark matter described by a k- essence Lagrangian Pd.; X_. We derive the effective coupling between such an imperfect- fluid dark matter and the gravitational sector under the quasistatic approximation on subhorizon scales. By considering the purely kinetic Lagrangian PdX_ as a particular case, the formalism is verified to reproduce the gravitational coupling of a perfect- fluid dark matter.

DOI

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62

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(Scopus)
Bosonic coherent motions in the Universe

Jihn E. Kim, Yannis K. Semertzidis, Shinji Tsujikawa

Frontiers of Physics 2 ( 60 ) 1 - 14 2014 [Refereed]

　View Summary

We review the role of fundamental spin-0 bosons as bosonic coherent motion (BCM) in the Universe. The fundamental spin-0 bosons have the potential to account for the baryon number generation, cold dark matter (CDM) via BCM, inflation, and dark energy. Among these, we pay particular attention to the CDM possibility because it can be experimentally tested with the current experimental techniques. We also comment on the panoply of the other roles of spin-0 bosons–such as those for cosmic accelerations at early and late times.

DOI

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20

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Super-renormalizable or finite completion of the Starobinsky theory

Fabio Briscese, Leonardo Modesto, Shinji Tsujikawa

PHYSICAL REVIEW D 89 ( 2 ) 1 - 13 2014.01 [Refereed]

　View Summary

The recent Planck data of cosmic microwave background temperature anisotropies support the Starobinsky theory in which the quadratic Ricci scalar drives cosmic inflation. We build up a multidimensional quantum consisted ultraviolet completion of the model in a phenomenological "bottom-up approach." We present the maximal class of theories compatible with unitarity and (super-)renormalizability or finiteness which reduces to the Starobinsky theory in the low-energy limit. The outcome is a maximal extension of the Krasnikov-Tomboulis-Modesto theory including an extra scalar degree of freedom besides the graviton field. The original theory was afterwards independently discovered by Biswas-Gerwick-Koivisto-Mazumdar starting from first principles. We explicitly show power counting super-renormalizability or finiteness (in odd dimensions) and unitarity (no ghosts) of the theory. Any further extension of the theory is nonunitary, confirming the existence of at most one single extra degree of freedom, the scalaron. A mechanism to achieve the Starobinsky theory in string (field) theory is also investigated at the end of the paper.

DOI

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61

Citation

(Scopus)
Observational signatures of anisotropic inflationary models

Junko Ohashi, Jiro Soda, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2013 ( 12 ) 1 - 30 2013.12 [Refereed]

DOI

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65

Citation

(Scopus)
Anisotropic power-law k-inflation

Junko Ohashi, Jiro Soda, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 88 ( 10 ) 1 - 11 2013.11 [Refereed]

DOI

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61

Citation

(Scopus)
Non-local massive gravity

Leonardo Modesto, Shinji Tsujikawa

PHYSICS LETTERS B 727 ( 1-3 ) 48 - 56 2013.11 [Refereed]

　View Summary

We present a general covariant action for massive gravity merging together a class of "non-polynomial" and super-renormalizable or finite theories of gravity with the non-local theory of gravity recently proposed by Jaccard, Maggiore and Mitsou (Phys. Rev. D 88 (2013) 044033). Our diffeomorphism invariant action gives rise to the equations of motion appearing in non-local massive gravity plus quadratic curvature terms. Not only the massive graviton propagator reduces smoothly to the massless one without a vDVZ discontinuity, but also our finite theory of gravity is unitary at tree level around the Minkowski background. We also show that, as long as the graviton mass m is much smaller the today's Hubble parameter H-0, a late-time cosmic acceleration can be realized without a dark energy component due to the growth of a scalar degree of freedom. In the presence of the cosmological constant Lambda, the dominance of the non-local mass term leads to a kind of "degravitation" for Lambda at the late cosmological epoch. (C) 2013 Elsevier B.V. All rights reserved.

DOI

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68

Citation

(Scopus)
Quintessence: a review

Shinji Tsujikawa

CLASSICAL AND QUANTUM GRAVITY 30 ( 21 ) 1 - 18 2013.11 [Refereed] [Invited]

DOI

Scopus

539

Citation

(Scopus)
Screening the fifth force in the Horndeski's most general scalar-tensor theories

Ryotaro Kase, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 08 ( 8 ) 1 - 36 2013.08 [Refereed]

　View Summary

We study how the Vainshtein mechanism operates in the most general scalartensor theories with second-order equations of motion. The field equations of motion, which can be also applicable to most of other screening scenarios proposed in literature, are generally derived in a spherically symmetric space-time with a matter source. In the presence of a field coupling to the Ricci scalar, we clarify conditions under which the Vainshtein mechanism is at work in a weak gravitational background. We also obtain the solutions of the field equation inside a spherically symmetric body and show how they can be connected to exterior solutions that accommodate the Vainshtein mechanism. We apply our general results to a number of concrete models such as the covariant/extended Galileons and the DBI Galileons with Gauss-Bonnet and other terms. In these models the fifth force can be suppressed to be compatible with solar-system constraints, provided that non-linear field kinetic terms coupled to the Einstein tensor do not dominate,. over other non-linear field self-interactions.

DOI

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59

Citation

(Scopus)
Planck constraints on single-field inflation

Shinji Tsujikawa, Junko Ohashi, Sachiko Kuroyanagi, Antonio De Felice

Physical Review D - Particles, Fields, Gravitation and Cosmology 88 ( 2 ) 2013.07 [Refereed]

DOI

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89

Citation

(Scopus)
Constraints on f(R) theory and Galileons from the latest data of galaxy redshift surveys

Hiroyuki Okada, Tomonori Totani, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 87 ( 10 ) 1 - 16 2013.05 [Refereed]

DOI

Scopus

43

Citation

(Scopus)
Anisotropic non-Gaussianity from a two-form field

Junko Ohashi, Jiro Soda, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 87 ( 8 ) 2013.04 [Refereed]

DOI

Scopus

63

Citation

(Scopus)
Anisotropic non-Gaussianity from a two-form field

Junko Ohashi, Jiro Soda, Shinji Tsujikawa

PHYSICAL REVIEW D 87 ( 8 ) 1 - 10 2013.04 [Refereed]

　View Summary

We study an inflationary scenario with a two-form field to which an inflaton couples nontrivially. First, we show that anisotropic inflation can be realized as an attractor solution and that the two-form hair remains during inflation. A statistical anisotropy can be developed because of a cumulative anisotropic interaction induced by the background two-form field. The power spectrum of curvature perturbations has a prolate-type anisotropy, in contrast to the vector models having an oblate-type anisotropy. We also evaluate the bispectrum and trispectrum of curvature perturbations by employing the in-in formalism based on the interacting Hamiltonians. We find that the nonlinear estimators f(NL) and tau(NL) are correlated with the amplitude g(*) of the statistical anisotropy in the power spectrum. Unlike the vector models, both f(NL) and tau(NL) vanish in the squeezed limit. However, the estimator f(NL) can reach the order of 10 in the equilateral and enfolded limits. These results are consistent with the latest bounds on f(NL) constrained by Planck. DOI: 10.1103/PhysRevD.87.083520

DOI

Scopus

63

Citation

(Scopus)
Observational constraints on quintessence: Thawing, tracker, and scaling models

Takeshi Chiba, Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 87 ( 8 ) 1 - 12 2013.04 [Refereed]

　View Summary

For two types of quintessence models having thawing and tracking properties, there exist analytic solutions for the dark energy equation of state w expressed in terms of several free parameters. We put observational bounds on the parameters in such scenarios by using the recent type Ia supernovae, cosmic microwave background, and baryon acoustic oscillations data. The observational constraints are quite different depending on whether or not the recent baryon acoustic oscillations data from BOSS are taken into account. With the BOSS data the upper bounds of today's values of w (= w(0)) in thawing models is very close to -1, whereas without this data the values of w(0) away from -1 can still be allowed. The tracker equation of state w((0)) during the matter era is constrained to be w((0)) < -0.949 at 95% C. L. even without the BOSS data, so that the tracker models with w away from -1 are severely disfavored. We also study observational constraints on scaling models in which w starts to evolve from 0 in the deep matter era and show that the transition to the equation of state close to w = -1 needs to occur at an early cosmological epoch. In the three classes of quintessence models studied in this paper, the past evolution of the Hubble parameters in the best-fit models shows only less than a 2.5% difference compared to Lambda CDM. DOI: 10.1103/PhysRevD.87.083505

DOI

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80

Citation

(Scopus)
Shapes of primordial non-Gaussianities in the Horndeski's most general scalar-tensor theories

Antonio De Felice, Shinji Tsujikawa

Journal of Cosmology and Astroparticle Physics 2013 ( 3 ) 1 - 38 2013.03 [Refereed]

DOI

Scopus

59

Citation

(Scopus)
DECIGO PATHFINDER

Masaki Ando, Shinji Tsujikawa, 他

INTERNATIONAL JOURNAL OF MODERN PHYSICS D 22 ( 1341002 ) 1 - 10 2013.01 [Refereed]
Testing for dynamical dark energy models with redshift-space distortions

Shinji Tsujikawa, Antonio De Felice, Jailson Alcaniz

Journal of Cosmology and Astroparticle Physics 2013 ( 1 ) 1 - 22 2013.01 [Refereed]

DOI

Scopus

31

Citation

(Scopus)
Potential-driven Galileon inflation

Junko Ohashi, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 10 ( 10 ) 1 - 31 2012.10 [Refereed]

DOI

Scopus

58

Citation

(Scopus)
Consistency of inflation and preheating in F(R) supergravity

Sergei V. Ketov, Shinji Tsujikawa

PHYSICAL REVIEW D 86 ( 2 ) 1 - 12 2012.07 [Refereed]

DOI

Scopus

39

Citation

(Scopus)
Observational constraints on dark energy with a fast varying equation of state

Antonio De Felice, Savvas Nesseris, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 05 ( 5 ) 1 - 19 2012.05 [Refereed]

DOI

Scopus

31

Citation

(Scopus)
Observational tests of inflation with a field derivative coupling to gravity

Shinji Tsujikawa

PHYSICAL REVIEW D 85 ( 8 ) 1 - 11 2012.04 [Refereed]

DOI

Scopus

110

Citation

(Scopus)
Cosmological constraints on extended Galileon models

Antonio De Felice, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 03 ( 3 ) 1 - 26 2012.03 [Refereed]

DOI

Scopus

55

Citation

(Scopus)
Vainshtein mechanism in second-order scalar-tensor theories

Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 85 ( 4 ) 2012.02 [Refereed]

DOI

Scopus

87

Citation

(Scopus)
Conditions for the cosmological viability of the most general scalar-tensor theories and their applications to extended Galileon dark energy models

Antonio De Felice, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 02 ( 2 ) 1 - 24 2012.02 [Refereed]

DOI

Scopus

192

Citation

(Scopus)
Generalized Galileon cosmology

Antonio De Felice, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 84 ( 12 ) 2011.12 [Refereed]

DOI

Scopus

143

Citation

(Scopus)
Generalized Galileon cosmology

Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 84 ( 12 ) 1 - 19 2011.12 [Refereed]

DOI

Scopus

143

Citation

(Scopus)
Effective gravitational couplings for cosmological perturbations in the most general scalar-tensor theories with second-order field equations

Antonio De Felice, Tsutomu Kobayashi, Shinji Tsujikawa

PHYSICS LETTERS B 706 ( 2-3 ) 123 - 133 2011.12 [Refereed]

　View Summary

In the Horndeski's most general scalar-tensor theories the equations of scalar density perturbations are derived in the presence of non-relativistic matter minimally coupled to gravity. Under a quasi-static approximation on sub-horizon scales we obtain the effective gravitational coupling G(eff) associated with the growth rate of matter perturbations as well as the effective gravitational potential Phi(eff) relevant to the deviation of light rays. We then apply our formulas to a number of modified gravitational models of dark energy - such as those based on f (R) theories, Brans-Dicke theories, kinetic gravity braidings, covariant Galileons, and field derivative couplings with the Einstein tensor. Our results are useful to test the large-distance modification of gravity from the future high-precision observations of large-scale structure, weak lensing, and cosmic microwave background. (C) 2011 Elsevier B.V. All rights reserved.

DOI

Scopus

210

Citation

(Scopus)
Observational test of inflation in loop quantum cosmology

Martin Bojowald, Gianluca Calcagni, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 11 ( 11 ) 1 - 31 2011.11 [Refereed]

DOI

Scopus

78

Citation

(Scopus)
Observational Constraints on Loop Quantum Cosmology

Martin Bojowald, Gianluca Calcagni, Shinji Tsujikawa

PHYSICAL REVIEW LETTERS 107 ( 21 ) 1 - 5 2011.11 [Refereed]

DOI

Scopus

105

Citation

(Scopus)
Inflationary non-Gaussianities in the most general second-order scalar-tensor theories

Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 84 ( 8 ) 1 - 15 2011.10 [Refereed]

DOI

Scopus

155

Citation

(Scopus)
Chaotic inflation in modified gravitational theories

Antonio De Felice, Shinji Tsujikawa, Joseph Elliston, Reza Tavakol

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 08 ( 8 ) 1 - 39 2011.08 [Refereed]

DOI

Scopus

51

Citation

(Scopus)
THERMODYNAMICS IN MODIFIED GRAVITY THEORIES

Kazuharu Bamba, Chao-Qiang Geng, Shinji Tsujikawa

INTERNATIONAL JOURNAL OF MODERN PHYSICS D 20 ( 8 ) 1363 - 1371 2011.08 [Refereed]

　View Summary

We demonstrate that there exists an equilibrium description of thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density f(R,phi,X), where R is the Ricci scalar and X is the kinetic energy of a scalar field phi. This comes from a suitable definition of an energy momentum tensor of the "dark" component obeying the local energy conservation law in the Jordan frame. It is shown that the equilibrium description in terms of the horizon entropy S is convenient because it takes into account the contribution of the horizon entropy (S) over cap S in non-equilibrium thermodynamics as well as an entropy production term.

DOI

Scopus

21

Citation

(Scopus)
Observational constraints on assisted k-inflation

Junko Ohashi, Shinji Tsujikawa

PHYSICAL REVIEW D 83 ( 10 ) 1 - 12 2011.05 [Refereed]

DOI

Scopus

13

Citation

(Scopus)
The Japanese space gravitational wave antenna: DECIGO

Seiji Kawamura, Masaki Ando, Naoki Seto, Shuichi Sato, Takashi Nakamura, Kimio Tsubono, Nobuyuki Kanda, Takahiro Tanaka, Jun'ichi Yokoyama, Ikkoh Funaki, Kenji Numata, Kunihito Ioka, Takeshi Takashima, Kazuhiro Agatsuma, Tomotada Akutsu, Koh-suke Aoyanagi, Koji Arai, Akito Araya, Hideki Asada, Yoichi Aso, Dan Chen, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Kiwamu Izumi, Isao Kawano, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Sachiko Kuroyanagi, Kei-ichi Maeda, Hideo Matsuhara, Nobuyuki Matsumoto, Yuta Michimura, Osamu Miyakawa, Umpei Miyamoto, Shinji Miyoki, Mutsuko Y. Morimoto, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Kazuhiro Nakazawa, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Kenshi Okada, Norio Okada, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Ryo Saito, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Ayaka Shoda, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Rieko Suzuki, Hideyuki Tagoshi, Fuminobu Takahashi, Kakeru Takahashi, Keitaro Takahashi, Ryutaro Takahashi, Ryuichi Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Takamori Akiteru, Tadashi Takano, Nobuyuki Tanaka, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Yasuo Torii, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Akitoshi Ueda, Ken-ichi Ueda, Masayoshi Utashima, Yaka Wakabayashi, Kent Yagi, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino, Ke-Xun Sun

CLASSICAL AND QUANTUM GRAVITY 28 ( 9 ) 1 - 12 2011.05 [Refereed]

DOI

Scopus

562

Citation

(Scopus)
Primordial non-gaussianities in general modified gravitational models of inflation

Antonio De Felice, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 04 ( 4 ) 1 - 37 2011.04 [Refereed]

DOI

Scopus

111

Citation

(Scopus)
Matter perturbations in Galileon cosmology

Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

PHYSICAL REVIEW D 83 ( 4 ) 1 - 15 2011.02 [Refereed]

DOI

Scopus

119

Citation

(Scopus)
Observational constraints on Galileon cosmology

Savvas Nesseris, Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 82 ( 12 ) 1 - 13 2010.12 [Refereed]

DOI

Scopus

130

Citation

(Scopus)
Chameleon dark energy models with characteristic signatures

Radouane Gannouji, Bruno Moraes, David F. Mota, David Polarski, Shinji Tsujikawa, Hans A. Winther

PHYSICAL REVIEW D 82 ( 12 ) 1 - 16 2010.12 [Refereed]

DOI

Scopus

60

Citation

(Scopus)
Cosmology of a Covariant Galileon Field

Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW LETTERS 105 ( 11 ) 1 - 4 2010.09 [Refereed]

DOI

Scopus

268

Citation

(Scopus)
Density perturbations in general modified gravitational theories

Antonio De Felice, Shinji Mukohyama, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 82 ( 2 ) 2010.07 [Refereed]

DOI

Scopus

103

Citation

(Scopus)
Density perturbations in general modified gravitational theories

Antonio De Felice, Shinji Mukohyama, Shinji Tsujikawa

PHYSICAL REVIEW D 82 ( 2 ) 1 - 14 2010.07 [Refereed]

DOI

Scopus

103

Citation

(Scopus)
Generalized Brans-Dicke theories

Antonio De Felice, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 07 ( 7 ) 1 - 19 2010.07 [Refereed]

DOI

Scopus

77

Citation

(Scopus)
The universe is accelerating. Do we need a new mass scale?

Savvas Nesseris, Federico Piazza, Shinji Tsujikawa

PHYSICS LETTERS B 689 ( 4-5 ) 122 - 128 2010.05 [Refereed]

　View Summary

We try to address quantitatively the question whether a new mass is needed to fit current supernovae data. For this purpose, we consider an infra-red modification of gravity that does not contain any new mass scale but systematic subleading corrections proportional to the curvature. The modifications are of the same type as the one recently derived by enforcing the "Ultra Strong Equivalence Principle" (USEP) upon a Friedmann-Lemaitre-Robertson-Walker universe in the presence of a scalar field. The distance between two comoving observers is altered by these corrections and the observations at high redshift are affected at any time during the cosmic evolution. While the specific values of the parameters predicted by USEP are ruled out, there are regions of parameter space that fit Snla data very well. This allows an interesting possibility to explain the apparent cosmic acceleration today without introducing either a dark energy component or a new mass scale. (C) 2010 Elsevier B.V. All rights reserved.

DOI

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3

Citation

(Scopus)
DECIGO and DECIGO pathfinder

Masaki Ando, Seiji Kawamura, Naoki Seto, Shuichi Sato, Takashi Nakamura, Kimio Tsubono, Takeshi Takashima, Ikkoh Funaki, Kenji Numata, Nobuyuki Kanda, Takahiro Tanaka, Kunihito Ioka, Kazuhiro Agatsuma, Koh-suke Aoyanagi, Koji Arai, Akito Araya, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Kiwamu Izumi, Isao Kawano, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Umpei Miyamoto, Shinji Miyoki, Mutsuko Y. Morimoto, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Kouji Nakamura, Masahiro Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Kazuhiro Nakazawa, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Kenshi Okada, Norio Okada, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Ryo Saito, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Rieko Suzuki, Hideyuki Tagoshi, Fuminobu Takahashi, Kakeru Takahashi, Keitaro Takahashi, Ryutaro Takahashi, Ryuichi Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Takamori Akiteru, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Yasuo Torii, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Akitoshi Ueda, Ken-ichi Ueda, Masayoshi Utashima, Yaka Wakabayashi, Kent Yagi, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino, Ken-Xun Sun

CLASSICAL AND QUANTUM GRAVITY 27 ( 8 ) 1 - 10 2010.04 [Refereed]

DOI

Scopus

50

Citation

(Scopus)
Equilibrium thermodynamics in modified gravitational theories

Kazuharu Bamba, Chao-Qiang Geng, Shinji Tsujikawa

PHYSICS LETTERS B 688 ( 1 ) 101 - 109 2010.04 [Refereed]

　View Summary

We show that it is possible to obtain a picture of equilibrium thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density f (R, phi, X), where R is the Ricci scalar and x is the kinetic energy of a scalar field phi. This comes from a suitable definition of an energy-momentum tensor of the "dark" component that respects to a local energy conservation in the Jordan frame. In this framework the horizon entropy S corresponding to equilibrium thermodynamics is equal to a quarter of the horizon area A in units of gravitational constant G, as in Einstein gravity. For a flat cosmological background with a decreasing Hubble parameter, S globally increases with time, as it happens for viable f (R) inflation and dark energy models. We also show that the equilibrium description in terms of the horizon entropy S is convenient because it takes into account the contribution of both the horizon entropy (S) over cap in non-equilibrium thermodynamics and an entropy production term. (C) 2010 Elsevier B.V. All rights reserved.

DOI

Scopus

78

Citation

(Scopus)
f (R) Theories

Antonio De Felice, Shinji Tsujikawa

LIVING REVIEWS IN RELATIVITY 13 ( 3 ) 1 - 161 2010 [Refereed] [Invited]

DOI

Scopus

3277

Citation

(Scopus)
Matter instabilities in general Gauss-Bonnet gravity

Antonio De Felice, David F. Mota, Shinji Tsujikawa

PHYSICAL REVIEW D 81 ( 2 ) 1 - 9 2010.01 [Refereed]

DOI

Scopus

69

Citation

(Scopus)
Assisted dark energy

Junko Ohashi, Shinji Tsujikawa

PHYSICAL REVIEW D 80 ( 10 ) 1 - 13 2009.11 [Refereed]

DOI

Scopus

26

Citation

(Scopus)
Dispersion of growth of matter perturbations in f(R) gravity

Shinji Tsujikawa, Radouane Gannouji, Bruno Moraes, David Polarski

PHYSICAL REVIEW D 80 ( 8 ) 1 - 11 2009.10 [Refereed]

DOI

Scopus

119

Citation

(Scopus)
Solar system constraints on f(G) gravity models

Antonio De Felice, Shinji Tsujikawa

PHYSICAL REVIEW D 80 ( 6 ) 1 - 15 2009.09 [Refereed]

DOI

Scopus

154

Citation

(Scopus)
DECIGO pathfinder

Masaki Ando, Seiji Kawamura, Shuichi Sato, Takashi Nakamura, Kimio Tsubono, Akito Araya, Ikkoh Funaki, Kunihito Ioka, Nobuyuki Kanda, Shigenori Moriwaki, Mitsuru Musha, Kazuhiro Nakazawa, Kenji Numata, Shin-ichiro Sakai, Naoki Seto, Takeshi Takashima, Takahiro Tanaka, Kazuhiro Agatsuma, Koh-suke Aoyanagi, Koji Arai, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Yumiko Ejiri, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Nobuki Kawashima, Fumiko Kawazoe, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shinji Mukohyama, Shigeo Nagano, Isao Naito, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Taiga Noumi, Yoshiyuki Obuchi, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Norio Okada, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Rieko Suzuki, Hideyuki Tagoshi, Fuminobu Takahashi, Kakeru Takahashi, Keitaro Takahashi, Ryutaro Takahashi, Ryuichi Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Takamori Akiteru, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Yasuo Torii, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Akitoshi Ueda, Ken-ichi Ueda, Masayoshi Utashima, Yaka Wakabayashi, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino

CLASSICAL AND QUANTUM GRAVITY 26 ( 9 ) 1 - 12 2009.05 [Refereed]

DOI

Scopus

20

Citation

(Scopus)
Chameleon scalar fields in relativistic gravitational backgrounds

Shinji Tsujikawa, Takashi Tamaki, Reza Tavakol

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 05 ( 5 ) 1 - 26 2009.05 [Refereed]

DOI

Scopus

57

Citation

(Scopus)
Construction of cosmologically viable f(G) gravity models

Antonio De Felice, Shinji Tsujikawa

PHYSICS LETTERS B 675 1 - 8 2009.04 [Refereed]
Equilibrium description of thermodynamics in modified gravitational theories

Kazuharu Bamba, Chao-Qiang Geng, Shinji Tsujikawa

Proceedings of the nineteenth workshop on general relativity and gravitation in Japan, edited by Motoyuki Saijo, Umpei Miyamoto, Tomohiro Harada, Misao Sasaki, Tetsuya Shiromizu, and Shinji Mukohyama 109 - 112 2009
Revisiting chameleon gravity: Thin-shell and no-shell fields with appropriate boundary conditions

Takashi Tamaki, Shinji Tsujikawa

PHYSICAL REVIEW D 78 ( 8 ) 1 - 11 2008.10 [Refereed]

DOI

Scopus

57

Citation

(Scopus)
Second-order matter density perturbations and skewness in scalar-tensor modified gravity models

Takayuki Tatekawa, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 0809 ( 009 ) 1 - 21 2008.09 [Refereed]

CiNii
Generic estimates for magnetic fields generated during inflation including Dirac-Born-Infeld theories

Kazuharu Bamba, Nobuyoshi Ohta, Shinji Tsujikawa

PHYSICAL REVIEW D 78 ( 4 ) 1 - 7 2008.08 [Refereed]

DOI

Scopus

40

Citation

(Scopus)
The effect of modified gravity on weak lensing

Shinji Tsujikawa, Takayuki Tatekawa

PHYSICS LETTERS B 665 ( 5 ) 325 - 331 2008.07 [Refereed]

　View Summary

We study the effect of modified gravity on weak lensing in a class of scalar-tensor theory that includes f(R) gravity as a special case. These models are designed to satisfy local gravity constraints by having a large scalar-field Mass in a region of high curvature. Matter density perturbations in these models are enhanced at small redshifts because of the presence of a coupling Q that characterizes the strength between dark energy and non-relativistic matter. We compute a convergence power spectrum of weak lensing numerically and show that the spectral index and the amplitude of the spectrum in the linear regime can be significantly modified compared to the Lambda CDM model for large values of vertical bar Q vertical bar Of the Order Of unity. Thus weak lensing provides a powerful tool to constrain such large coupling scalar-tensor models including f(R) gravity. (c) 2008 Elsevier B.V. All rights reserved.

DOI

Scopus

61

Citation

(Scopus)
Constraints on scalar-tensor models of dark energy from observational and local gravity tests

Shinji Tsujikawa, Kotub Uddin, Shuntaro Mizuno, Reza Tavakol, Jun'Ichi Yokoyama

Physical Review D - Particles, Fields, Gravitation and Cosmology 77 ( 10 ) 2008.05 [Refereed]

DOI

Scopus

142

Citation

(Scopus)
Constraints on scalar-tensor models of dark energy from observational and local gravity tests

Shinji Tsujikawa, Kotub Uddin, Shuntaro Mizuno, Reza Tavakol, Jun'ichi Yokoyama

PHYSICAL REVIEW D 77 ( 10 ) 1 - 19 2008.05 [Refereed]

DOI

Scopus

142

Citation

(Scopus)
Solar system and equivalence principle constraints on f(R) gravity by the chameleon approach

Salvatore Capozziello, Shinji Tsujikawa

PHYSICAL REVIEW D 77 ( 10 ) 1 - 4 2008.05 [Refereed]

DOI

Scopus

261

Citation

(Scopus)
Density perturbations in f(R) gravity theories in metric and Palatini formalisms

Shinji Tsujikawa, Kotub Uddin, Reza Tavakol

PHYSICAL REVIEW D 77 ( 4 ) 1 - 27 2008.02 [Refereed]

DOI

Scopus

113

Citation

(Scopus)
Second-order matter density perturbations and skewness in scalar-tensor modified gravity models

T.Tatekawa, S.Tsujikawa

JCAP 09 009 2008 [Refereed]

DOI

Scopus

22

Citation

(Scopus)
Observational signatures of f(R) dark energy models that satisfy cosmological and local gravity constraints

Shinji Tsujikawa

PHYSICAL REVIEW D 77 ( 2 ) 1 - 13 2008.01 [Refereed]

DOI

Scopus

436

Citation

(Scopus)
Phantom crossing, equation-of-state singularities, and local gravity constraints in f(R) models

Luca Amendola, Shinji Tsujikawa

PHYSICS LETTERS B 660 125 - 132 2008.01 [Refereed]
The Japanese Space Gravitational Wave Antenna; DECIGO

Seiji Kawamura, Masaki Ando, Takashi Nakamura, Kimio Tsubono, Takahiro Tanaka, Ikkoh Funaki, Naoki Seto, Kenji Numata, Shuichi Sato, Kunihito Ioka, Nobuyuki Kanda, Takeshi Takashima, Kazuhiro Agatsuma, Tomotada Akutsu, Tomomi Akutsu, Koh-suke Aoyanagi, Koji Arai, Yuta Arase, Akito Araya, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Shogo Kamagasako, Nobuki Kawashima, Fumiko Kawazoe, Hiroyuki Kirihara, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Noriyasu Nakagawa, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Akira Okutomi, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Hideyuki Tagoshi, Kakeru Takahashi, Keitaro Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Ryuichi Takahashi, Ryutaro Takahashi, Akiteru Takamori, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Mitsuru Tokuda, Masao Tokunari, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Ken-ichi Ueda, Masayoshi Utashima, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino

TAUP2007: TENTH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS 120 125 - 131 2008 [Refereed]

DOI

Scopus

26

Citation

(Scopus)
Prospects of inflation in delicate D-brane cosmology

Sudhakar Panda, M. Sami, Shinji Tsujikawa

PHYSICAL REVIEW D 76 ( 10 ) 1 - 12 2007.11 [Refereed]

DOI

Scopus

55

Citation

(Scopus)
Power-laws f(R) theories are cosmologically unacceptable

Luca Amendola, David Polarski, Shinji Tsujikawa

INTERNATIONAL JOURNAL OF MODERN PHYSICS D 16 ( 10 ) 1555 - 1561 2007.10 [Refereed]

　View Summary

In a recent paper, 1 we have shown that f(R) = R + mu R-n modified gravity dark energy models are not cosmologically viable because during the matter era that precedes the accelerated stage the cosmic expansion is given by a similar to t(1/2) rather than a similar to t(2/3), where a is a scale factor and t is the cosmic time. A recent work by Capozziello et al.(2) criticized our results presenting some apparent counter-examples to our claim in f(R) = mu R-n models. We show here that those particular R-n models can produce an expansion as a similar to t(2/3) but this does not connect to a late-time acceleration. Hence, though acceptable f(R) dark energy models might exist, the R-n models presented in Capozziello et al. are not cosmologically viable, confirming our previous results in Ref. 1.
暗黒エネルギーの起源は何か

Shinji Tsujikawa

天文月報 ( 9月 ) 462 - 472 2007.09 [Refereed] [Invited]
Ultraviolet stable, Lorentz-violating dark energy with transient phantom era

Maxim Libanov, Valery Rubakov, Eleftherios Papantonopoulos, M. Sami, Shinji Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 0708 ( 8 ) 1 - 29 2007.08 [Refereed]

DOI
Probing the coupling between dark components of the universe

Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 76 ( 2 ) 2007.07 [Refereed]

DOI

Scopus

360

Citation

(Scopus)
Matter density perturbations and effective gravitational constant in modified gravity models of dark energy

Shinji Tsujikawa

PHYSICAL REVIEW D 76 ( 2 ) 1 - 11 2007.07 [Refereed]

DOI

Scopus

263

Citation

(Scopus)
Probing the coupling between dark components of the universe

Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa

PHYSICAL REVIEW D 76 ( 2 ) 1 - 9 2007.07 [Refereed]

DOI

Scopus

360

Citation

(Scopus)
Conditions for the cosmological viability of f(R) dark energy models

Luca Amendola, Radouane Gannouji, David Polarski, Shinji Tsujikawa

PHYSICAL REVIEW D 75 ( 8 ) 1 - 22 2007.04 [Refereed]

DOI

Scopus

669

Citation

(Scopus)
f(R) gravity theories in Palatini formalism: Cosmological dynamics and observational constraints

Stephane Fay, Reza Tavakol, Shinji Tsujikawa

PHYSICAL REVIEW D 75 ( 6 ) 1 - 16 2007.03 [Refereed]

DOI

Scopus

155

Citation

(Scopus)
Are f(R) dark energy models cosmologically viable?

Luca Amendola, David Polarski, Shinji Tsujikawa

PHYSICAL REVIEW LETTERS 98 ( 13 ) 1 - 4 2007.03 [Refereed]

DOI

Scopus

476

Citation

(Scopus)
Realizing scale-invariant density perturbations in low-energy effective string theory

Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 75 ( 2 ) 2007 [Refereed]

DOI

Scopus

48

Citation

(Scopus)
Realizing scale-invariant density perturbations in low-energy effective string theory

Zong-Kuan Guo, Nobuyoshi Ohta, Shinji Tsujikawa

PHYSICAL REVIEW D 75 ( 2 ) 1 - 13 2007.01 [Refereed]

DOI

Scopus

48

Citation

(Scopus)
String-inspired cosmology: a late time transition from a scaling matter era to a dark energy universe caused by a Gauss-Bonnet coupling

Shinji Tsujikawa, M. Sami

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 0701 ( 1 ) 1 - 25 2007.01 [Refereed]

DOI

Scopus

89

Citation

(Scopus)
Dynamics of dark energy

Edmund J. Copeland, M. Sami, Shinji Tsujikawa

INTERNATIONAL JOURNAL OF MODERN PHYSICS D 15 ( 11 ) 1753 - 1935 2006.11 [Refereed] [Invited]
Avoidance of future singularities in loop quantum cosmology

M. Sami, Parampreet Singh, Shinji Tsujikawa

PHYSICAL REVIEW D 74 ( 4 ) 1 - 6 2006.08 [Refereed]

DOI

Scopus

139

Citation

(Scopus)
Challenges for scaling cosmologies

Luca Amendola, Miguel Quartin, Shinji Tsujikawa, Ioav Waga

PHYSICAL REVIEW D 74 ( 2 ) 1 - 14 2006.07 [Refereed]

DOI

Scopus

137

Citation

(Scopus)
General analytic formulas for attractor solutions of scalar-field dark energy models and their multifield generalizations

Shinji Tsujikawa

PHYSICAL REVIEW D 73 ( 10 ) 1 - 11 2006.05 [Refereed]

DOI

Scopus

81

Citation

(Scopus)
Cosmologies from higher-order string corrections

S Tsujikawa

ANNALEN DER PHYSIK 15 ( 4-5 ) 302 - 315 2006.04 [Refereed]

　View Summary

We study cosmologies based on low-energy effective string theory with higher-order string corrections to a tree-level action and with a modulus scalar field (dilaton or compactification modulus). In the presence of such corrections it is possible to construct nonsingular cosmological solutions in the context of Pre-Big-Bang and Ekpyrotic universes. We review the construction of nonsingular bouncing solutions and resulting density perturbations in Pre-Big-Bang and Ekpyrotic models. We also discuss the effect of higher-order string corrections on a dark energy universe and show several interesting possibilities of the avoidance of future singularities. (C) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI

Scopus

16

Citation

(Scopus)
Inflation from D3-brane motion in the background of D5-branes

S Panda, M Sami, S Tsujikawa, J Ward

PHYSICAL REVIEW D 73 ( 8 ) 1 - 10 2006.04 [Refereed]

DOI

Scopus

21

Citation

(Scopus)
Chaotic dynamics in preheating after inflation

Y Jin, S Tsujikawa

CLASSICAL AND QUANTUM GRAVITY 23 ( 2 ) 353 - 371 2006.01 [Refereed]

DOI

Scopus

13

Citation

(Scopus)
Inflation dynamics and reheating

Bruce A. Bassett, Shinji Tsujikawa, David Wands

Reviews of Modern Physics 78 ( 2 ) 537 - 589 2006 [Refereed] [Invited]

DOI

Scopus

869

Citation

(Scopus)
Inflation and dark energy arising from geometrical tachyons

S Panda, M Sami, S Tsujikawa

PHYSICAL REVIEW D 73 ( 2 ) 1 - 11 2006.01 [Refereed]

DOI

Scopus

46

Citation

(Scopus)
Phantom damping of matter perturbations

L Amendola, S Tsujikawa, M Sami

PHYSICS LETTERS B 632 ( 2-3 ) 155 - 158 2006.01 [Refereed]

　View Summary

Cosmological scaling solutions are particularly important in solving the coincidence problem of dark energy. We derive the equations of sub-Hubble linear matter perturbations for a general scalar-field Lagrangian-including quintessence, tachyon, dilatonic ghost condensate and k-essence-and solve them analytically for scaling solutions. We find that matter perturbations are always damped if a phantom field is coupled to dark matter and identify the cases in which the gravitational potential is constant. This provides an interesting possibility to place stringent observational constraints on scaling dark energy models. (c) 2005 Elsevier B.V. All rights reserved.

DOI

Scopus

101

Citation

(Scopus)
Dark energy and cosmological solutions in second-order string gravity

G Calcagni, S Tsujikawa, M Sami

CLASSICAL AND QUANTUM GRAVITY 22 ( 19 ) 3977 - 4006 2005.10 [Refereed]

　View Summary

We study the cosmological evolution based on a D-dimensional action in low-energy effective string theory in the presence of second-order curvature corrections and a modulus scalar field (a dilaton or compactification modulus). A barotropic perfect fluid coupled to the scalar field is also allowed. Phase space analysis and the stability of asymptotic solutions are performed for a number of models which include (i) a fixed scalar field, (ii) a linear dilaton in the string frame, and (iii) a logarithmic modulus in the Einstein frame. We confront analytical solutions with observational constraints for the deceleration parameter and show that Gauss-Bonnet gravity alone (i.e., with no matter fields) may not explain the current acceleration of the universe. We also study the future evolution of the universe using the Gauss-Bonnet parametrization and find that big rip singularities can be avoided even in the presence of a phantom fluid because of the balance between the fluid and curvature corrections. A non-minimal coupling between the fluid and the modulus field also opens up the interesting possibility of avoiding a big rip regardless of the details of the fluid equation of state.

DOI

Scopus

161

Citation

(Scopus)
Reconstruction of general scalar-field dark energy models

S Tsujikawa

PHYSICAL REVIEW D 72 ( 8 ) 1 - 8 2005.10 [Refereed]

DOI

Scopus

72

Citation

(Scopus)
Dynamics of assisted quintessence

SA Kim, AR Liddle, S Tsujikawa

PHYSICAL REVIEW D 72 ( 4 ) 1 - 6 2005.08 [Refereed]

DOI

Scopus

45

Citation

(Scopus)
The fate of (phantom) dark energy universe with string curvature corrections

M. Sami, Alexey Toporensky, Peter V. Tretjakov, Shinji Tsujikawa

PHYSICS LETTERS B 619 193 - 200 2005.06 [Refereed]
Coupled dark energy: towards a general description of the dynamics

B Gumjudpai, T Naskar, M Sami, S Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 06 ( 6 ) 1 - 29 2005.06 [Refereed]

DOI

Scopus

183

Citation

(Scopus)
Constraints on Dirac-Born-Infeld type dark energy models from varying alpha

Mohammad R. Garousi, M. Sami, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 71 ( 8 ) 1 - 11 2005.04 [Refereed]

DOI

Scopus

41

Citation

(Scopus)
Constraints on Dirac-Born-Infeld type dark energy models from varying alpha

MR Garousi, M Sami, S Tsujikawa

PHYSICAL REVIEW D 71 ( 8 ) 1 - 11 2005.04 [Refereed]

DOI

Scopus

41

Citation

(Scopus)
ループ量子宇宙論

Shinji Tsujikawa

数理科学 52 - 57 2005.04 [Refereed] [Invited]
Testing for double inflation with WMAP

David Parkinson, Shinji Tsujikawa, Bruce A. Bassett, Luca Amendola

Physical Review D - Particles, Fields, Gravitation and Cosmology 71 ( 6 ) 1 - 7 2005.03 [Refereed]

DOI

Scopus

50

Citation

(Scopus)
Properties of singularities in the (phantom) dark energy universe

S Nojiri, SD Odintsov, S Tsujikawa

PHYSICAL REVIEW D 71 ( 6 ) 1 - 16 2005.03 [Refereed]

DOI

Scopus

1128

Citation

(Scopus)
Testing for double inflation with WMAP

D Parkinson, S Tsujikawa, BA Bassett, L Amendola

PHYSICAL REVIEW D 71 ( 6 ) 1 - 7 2005.03 [Refereed]

DOI

Scopus

50

Citation

(Scopus)
What is needed of a tachyon if it is to be the dark energy?

EJ Copeland, MR Garousi, M Sami, S Tsujikawa

PHYSICAL REVIEW D 71 ( 4 ) 1 - 11 2005.02 [Refereed]

DOI

Scopus

252

Citation

(Scopus)
What is needed of a tachyon if it is to be the dark energy?

Edmund J. Copeland, Mohammad R. Garousi, M. Sami, Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 71 ( 4 ) 1 - 43003 2005 [Refereed]

DOI

Scopus

252

Citation

(Scopus)
Generation of electromagnetic fields in string cosmology with a massive scalar field on the anti-D-brane

Mohammad R. Garousi, M. Sami, Shinji Tsujikawa

PHYSICS LETTERS B 606 1 - 6 2004.11 [Refereed]
Observational constraints on patch inflation in noncommutative spacetime

G Calcagni, S Tsujikawa

PHYSICAL REVIEW D 70 ( 10 ) 1 - 16 2004.11 [Refereed]

DOI

Scopus

65

Citation

(Scopus)
A unified approach to scaling solutions in a general cosmological background

Shinji Tsujikawa, M. Sami

PHYSICS LETTERS B 603 113 - 123 2004.11 [Refereed]
Loop quantum gravity effects on inflation and the CMB

Shinji Tsujikawa, Parampreet Singh, Roy Maartens

CLASSICAL AND QUANTUM GRAVITY 21 5767 - 5775 2004.11 [Refereed]
Observational constraints on braneworld inflation: The effect of a Gauss-Bonnet term

S Tsujikawa, M Sami, R Maartens

PHYSICAL REVIEW D 70 ( 6 ) 1 - 10 2004.09 [Refereed]

DOI

Scopus

61

Citation

(Scopus)
Inflation in string-inspired cosmology and suppression of CMB low multipoles

Yun-song Piao, Shinji Tsujikawa, Xinmin Zhang

CLASSICAL AND QUANTUM GRAVITY 21 4455 - 4461 2004.08 [Refereed]
Cosmology from a rolling massive scalar field on the anti-D3 brane of de Sitter vacua

MR Garousi, M Sami, S Tsujikawa

PHYSICAL REVIEW D 70 ( 4 ) 1 - 12 2004.08 [Refereed]

DOI

Scopus

74

Citation

(Scopus)
Dilatonic ghost condensate as dark energy

F Piazza, S Tsujikawa

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 06 ( 7 ) 1 - 25 2004.07 [Refereed]

DOI

Scopus

196

Citation

(Scopus)
Density perturbations in generalized Einstein scenarios and constraints on nonminimal couplings from the cosmic microwave background

S Tsujikawa, B Gumjudpai

PHYSICAL REVIEW D 69 ( 12 ) 1 - 11 2004.06 [Refereed]

DOI

Scopus

118

Citation

(Scopus)
Constraints on braneworld inflation from CMB anisotropies

S Tsujikawa, AR Liddle

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 03 ( 3 ) 1 - 21 2004.03 [Refereed]

DOI

Scopus

55

Citation

(Scopus)
Observational constraints on braneworld inflation: The effect of a Gauss-Bonnet term

Shinji Tsujikawa, M. Sami, Roy Maartens

Physical Review D - Particles, Fields, Gravitation and Cosmology 70 ( 6 ) 10 2004 [Refereed]

DOI

Scopus

61

Citation

(Scopus)
Observational constraints on braneworld inflation: The effect of a Gauss-Bonnet term

Shinji Tsujikawa, M. Sami, Roy Maartens

Physical Review D - Particles, Fields, Gravitation and Cosmology 70 ( 6 ) 1 - 63525 2004 [Refereed]

DOI

Scopus

61

Citation

(Scopus)
Non-commutative inflation and the CMB

S Tsujikawa, R Maartens, R Brandenberger

PHYSICS LETTERS B 574 ( 3-4 ) 141 - 148 2003.11 [Refereed]

DOI

Scopus

137

Citation

(Scopus)
Noncommutative inflation and the CMB multipoles

QG Huang, M Li

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS 574 ( 11 ) 141 - 148 2003.11 [Refereed]
Cosmological density perturbations from perturbed couplings

S Tsujikawa

PHYSICAL REVIEW D 68 ( 8 ) 1 - 5 2003.10 [Refereed]

DOI

Scopus

23

Citation

(Scopus)
MSW-resonant fermion mixing during reheating

T Kanai, S Tsujikawa

NUCLEAR PHYSICS B 670 ( 1-2 ) 289 - 306 2003.10 [Refereed]

　View Summary

We study the dynamics of reheating in which an inflaton field couples two flavor fermions through Yukawa-couplings. When two fermions have a mixing term with a constant coupling, we show that the Mikheyev-Smirnov-Wolfenstein (MSW)-type resonance emerges due to a time-dependent background in addition to the standard fermion creation via parametric resonance. This MSW resonance not only alters the number densities of fermions generated by a preheating process but also can lead to the larger energy transfer from the inflaton to fermions. Our mechanism can provide additional source terms for the creation of superheavy fermions which may be relevant for the leptogenesis scenario. (C) 2003 Elsevier B.V. All rights reserved.

DOI

Scopus

1

Citation

(Scopus)
Aspects of string-gas cosmology at finite temperature

BA Bassett, M Borunda, M Serone, S Tsujikawa

PHYSICAL REVIEW D 67 ( 12 ) 1 - 12 2003.06 [Refereed]

DOI

Scopus

64

Citation

(Scopus)
Construction of nonsingular cosmological solutions in string theories

Shinji Tsujikawa

CLASSICAL AND QUANTUM GRAVITY 20 1991 - 2014 2003.05 [Refereed]
Correlation-consistency cartography of the double-inflation landscape

S Tsujikawa, D Parkinson, BA Bassett

PHYSICAL REVIEW D 67 ( 8 ) 1 - 20 2003.04 [Refereed]

DOI

Scopus

86

Citation

(Scopus)
Construction of nonsingular pre-big-bang and ekpyrotic cosmologies and the resulting density perturbations

S Tsujikawa, R Brandenberger, F Finelli

PHYSICAL REVIEW D 66 ( 8 ) 1 - 20 2002.10 [Refereed]

DOI

Scopus

165

Citation

(Scopus)
When can preheating affect the CMB?

Shinji Tsujikawa, Bruce A. Bassett

PHYSICS LETTERS B 536 ( 2002 ) 9 - 17 2002.06 [Refereed]
Nature of singularities in anisotropic string cosmology

A Toporensky, S Tsujikawa

PHYSICAL REVIEW D 65 ( 12 ) 1 - 15 2002.06 [Refereed]

DOI

Scopus

35

Citation

(Scopus)
Density perturbations in the ekpyrotic Universe and string-inspired generalizations

S Tsujikawa

PHYSICS LETTERS B 526 ( 3-4 ) 179 - 185 2002.02 [Refereed]

　View Summary

We study density perturbations in several cosmological models motivated by string theory. The evolution and the spectra of curvature perturbations R are analyzed in the ekpyrotic scenario and nonsingular string cosmologies. We find that these string-inspired models generally exhibit blue spectra in contrast to standard slow-roll inflationary scenarios. We also clarify the parameter range where R is enhanced on superhorizon scales. (C) 2002 Elsevier Science B.V. All rights reserved.
Fermion production from preheating-amplified metric perturbations

Bruce A. Bassett, Marco Peloso, Lorenzo Sorbo, Shinji Tsujikawa

NUCLEAR PHYSICS B 622 393 - 415 2002.01 [Refereed]
Cosmological perturbations from multi-field inflation in generalized Einstein theories

Alexei A. Starobinsky, Shinji Tsujikawa, Jun'ichi Yokoyama

NUCLEAR PHYSICS B 610 383 - 410 2001.08 [Refereed]
Brane preheating

S Tsujikawa, K Maeda, S Mizuno

PHYSICAL REVIEW D 63 ( 12 ) 2001.06 [Refereed]
Massive fermion production in nonsingular superstring cosmology

Shinji Tsujikawa, Hiroki Yajima

Physical Review D 64 ( 2 ) 1 - 5 2001 [Refereed]

DOI

Scopus

9

Citation

(Scopus)
Brane preheating

Shinji Tsujikawa, Kei-Ichi Maeda, Shuntaro Mizuno

Physical Review D 63 ( 12 ) 1 - 5 2001 [Refereed]

DOI

Scopus

19

Citation

(Scopus)
Preheating-cosmic magnetic dynamo?

Bruce A. Bassett, Giuseppe Pollifrone, Shinji Tsujikawa, Fermin Viniegra

Physical Review D 63 ( 10 ) 1 - 13 2001 [Refereed]

DOI

Scopus

3

Citation

(Scopus)
Inflationary preheating and primordial black holes

Bruce A. Bassett, Shinji Tsujikawa

Physical Review D 63 ( 12 ) 1 - 7 2001 [Refereed]

DOI
New constraints on multifield inflation with nonminimal coupling

Shinji Tsujikawa, Hiroki Yajima

PHYSICAL REVIEW D 62 ( 123512 ) 1 - 13 2000.11 [Refereed]
Multi-field fermionic preheating

S Tsujikawa, BA Bassett, F Viniegra

JOURNAL OF HIGH ENERGY PHYSICS 08 ( 8 ) 1 - 28 2000.08 [Refereed]
Preheating with extra dimensions

S Tsujikawa

JOURNAL OF HIGH ENERGY PHYSICS 07 ( 7 ) 1 - 25 2000.07 [Refereed]
Power-law inflation with a nonminimally coupled scalar field

Shinji Tsujikawa

PHYSICAL REVIEW D 62 ( 043512 ) 1 - 7 2000.07 [Refereed]
New twist to preheating

Shinji Tsujikawa, Bruce A. Bassett

PHYSICAL REVIEW D 62 ( 043510 ) 1 - 5 2000.07 [Refereed]
Spinodal effect in the natural inflation model

Shinji Tsujikawa, Takashi Torii

PHYSICAL REVIEW D 62 ( 043505 ) 1 - 9 2000.07 [Refereed]
Preheating of the nonminimally coupled inflaton field

Shinji Tsujikawa, Takashi Torii, Kei-ichi Maeda

PHYSICAL REVIEW D 61 ( 103501 ) 1 - 13 2000.04 [Refereed]
New constraints on multifield inflation with nonminimal coupling

Shinji Tsujikawa, Hiroki Yajima

Physical Review D - Particles, Fields, Gravitation and Cosmology 62 ( 12 ) 13 2000 [Refereed]

DOI

Scopus

49

Citation

(Scopus)
Particle production in the oscillating inflation model

Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 61 ( 8 ) 1 - 12 2000 [Refereed]

DOI

Scopus

6

Citation

(Scopus)
Are Kaluza-Klein modes enhanced by parametric resonance?

Shinji Tsujikawa

Physical Review D - Particles, Fields, Gravitation and Cosmology 61 ( 12 ) 1 - 9 2000 [Refereed]

DOI

Scopus

4

Citation

(Scopus)
Preheating with nonminimally coupled scalar fields in higher-curvature inflation models

S Tsujikawa, K Maeda, T Torii

PHYSICAL REVIEW D 60 ( 12 ) 1999.12 [Refereed]
Resonant particle production with nonminimally coupled scalar fields in preheating after inflation

Shinji Tsujikawa, Takashi Torii, Kei-ichi Maeda

PHYSICAL REVIEW D 60 ( 063515 ) 1 - 19 1999.08 [Refereed]

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Books and Other Publications

The Gravity of Math

Steve Nadis, Shing-Tung Yau, Shinji Tsujikawa( Part： Supervisor (editorial))

2024.08 ISBN: 4799112511

ASIN
Introduction to Modern Cosmology: From Inflation to Dark Energy

Shinji Tsujikawa( Part： Sole author)

2022.01 ISBN: 4065266319

ASIN
Encyclopedia of Relativity and Cosmology

( Part： Joint author)

2020.06 ISBN: 4254131283

ASIN
Handbook of Astrophysics

( Part： Joint author)

2020.02 ISBN: 4254131275

ASIN
The Encyclopedia of Cosmology Volume 3: Dark Energy

Shinji Tsujikawa( Part： Sole author, Volume 3)

World Scientific 2018.05 ISBN: 9814656194

ASIN
SUPER Science: The future of the universe predicted by relativity

Shinji Tsujikawa( Part： Sole author)

2015.02 ISBN: 4863541635

ASIN
Modifications of Einstein's theory of gravity at large distances

Tsujikawa, S., Papantonopoulos, E.( Part： Joint author)

Springer 2015 ISBN: 9783319100692
Lecture on Modern Cosmology

( Part： Sole author)

2013.07
Quantum Gravity and Quantum Cosmology

S. Tsujikawa, G. Calcagni, L. Papantonopoulos, G. Siopsis, N. Tsamis( Part： Joint author)

Springer 2013.01 ISBN: 9783642330360
Dark matter and dark energy : a challenger for modern cosmology

Matarrese, Sabino, Colpi, Monica, Gorini, Vittorio, Moschella, Ugo

Springer 2011.02 ISBN: 9789048186846

ASIN
Dark energy : theory and observations

Amendola, Luca, Tsujikawa, Shinji

Cambridge University Press 2010.06 ISBN: 0521516005

ASIN
Lectures on cosmology : accelerated expansion of the Universe

Wolschin, Georg

Springer 2010.03 ISBN: 3642105971

ASIN

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Presentations

Effective field theory of coupled dark energy and dark matter

Shinji Tsujikawa [Invited]

International Workshop on New Opportunities for Particle Physics 2025

Presentation date： 2025.07

Event date：
2025.07

　

　
Effective field theory of coupled dark energy and dark matter

Shinji Tsujikawa [Invited]

International Conference on Cosmology in Shanghai

Presentation date： 2025.05

Event date：
2025.05

-

2025.06
Stability of nonsingular black holes

Shinji Tsujikawa

2nd Bangkok workshop on Gravity and Cosmology

Presentation date： 2025.01
Coupled dark energy and dark matter with energy and momentum transfers

Shinji Tsujikawa [Invited]

CosmoGravitas

Presentation date： 2024.06
ダークエネルギーとダークマターが運動量とエネルギー交換による相互作用を持つ模型に対する，観測的な制限

辻川信二

日本物理学会

Presentation date： 2024.03
Gravitational wave constraints on scalar-tensor gravity from black hole and neutron star mergers

Shinji Tsujikawa

Gravity and Cosmology 2024

Presentation date： 2024.02
Gravitational wave constraints on scalar-tensor gravity from black hole and neutron star mergers

Shinji Tsujikawa

Bangkok workshop on gravity and cosmology

Presentation date： 2024.01
Constraining Horndeski theories with gravitational waves from coalescing binaries

Shinji Tsujikawa [Invited]

i-LINK workshop on observational cosmology

Presentation date： 2023.06
Linear stability of black holes with static scalar hair in full Horndeski theories: generic instabilities and surviving models

Shinji Tsujikawa

GR23

Presentation date： 2022.07
Interacting dark energy and dark matter with energy and momentum transfers

Shinji Tsujikawa [Invited]

Current Status of Cosmology

Presentation date： 2022.06
ホルンデスキ理論における相対論的天体の摂動論

辻川信二

日本物理学会

Presentation date： 2022.03
Stabilities of black hole solutions in vector-tensor theories

Shinji Tsujikawa [Invited]

SUSY2021

Presentation date： 2021.08
Weak gravity in dark energy with energy and momentum couplings

Shinji Tsujikawa [Invited]

Quarks

Presentation date： 2021.06
Modified gravity theories with application to cosmology

Shinji Tsujikawa [Invited]

XXI Jorge Andre Swieca School on Particles and Fields

Presentation date： 2021.02
Scaling solutions and weak gravity in dark energy with energy and momentum couplings

Shinji Tsujikawa [Invited]

J-PAS meeting

Presentation date： 2020.09
Tenth Aegean Summer School

Shinji Tsujikawa [Invited]

Tenth Aegean Summer School

Presentation date： 2019.09
Dark energy

Shinji Tsujikawa [Invited]

The 5th Tah Poe School on Cosmology

Presentation date： 2019.07
Dark energy in scalar-tensor versus vector-tensor theories

Shinji Tsujikawa [Invited]

2019 CCNU - cfa@USTC Junior Cosmology Symposium (Wuhan, China)

Presentation date： 2019.04
スペース重力波アンテナDECIGO計画 (100)：B-DECIGOの概要

安東正樹, 辻川信二

日本物理学会 (九州大学)

Presentation date： 2019.03
ベクトル・テンソル理論に基づく暗黒エネルギー模型に対する積分ザックス・ヴォルフェ効果からの制限

中村進太郎, Antonio De Felice, 加瀬竜太郎, 辻川信二

日本物理学会 (九州大学)

Presentation date： 2019.03
Gauge-ready formulation of cosmological perturbations in scalar-vector-tensor theories

Lavinia Heisenberg, 加瀬竜太郎, 辻川信二

日本物理学会 (九州大学)

Presentation date： 2019.03
Dark energy in scalar-tensor versus vector-tensor theories

Shinji Tsujikawa [Invited]

PHILOSOPHY OF DARK ENERGY WORKSHOP (アーバイン (米国))

Presentation date： 2019.03
Galaxy-ISW constraints on dark energy models consistent with GW170817

Shinji Tsujikawa, Shintaro Nakamura, Antonio De Felice, Ryotaro Kase

TESTING GRAVITY 2019 (バンクーバー，カナダ)

Presentation date： 2019.01
Dark energy in scalar-tensor and vector-tensor theories after GW170817

Shinji Tsujikawa [Invited]

5th International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Asymmetry (Kaohsiung, Taiwan)

Presentation date： 2018.12
Cosmology in scalar-vector-tensor theories

Shinji Tsujikawa, Lavinia Heisenberg, Ryotaro Kase [Invited]

5th Korea-Japan Workshop on Dark Energy: Starobinsky's Universe (大田，韓国)

Presentation date： 2018.08
Dark energy scenario consistent with GW170817 in theories beyond Horndeski gravity

Shinji Tsujikawa [Invited]

Fifteenth Marcel Grossmann Meeting (ローマ・ローマ大学)

Presentation date： 2018.07
Cosmology in scalar-vector-tensor theories

Shinji Tsujikawa [Invited]

Essential next steps for gravity and cosmology (仙台・東北大学)

Presentation date： 2018.06
Hairy black holes and gravitational waves in vector-tensor theories

Shinji Tsujikawa [Invited]

Gravitational waves in modified gravity (チューリッヒ，スイス)

Presentation date： 2018.05
スペース重力波アンテナDECIGO計画 (90)：DECIGO/B-DECIGOの概要

安東正樹, 辻川信二

日本物理学会 (野田，東京理科大学)

Presentation date： 2018.03
物質場と直接結合したgeneralized Proca理論における第5の力の抑制

中村進太郎, 加瀬竜太郎, 辻川信二

日本物理学会 (野田市，東京理科大学)

Presentation date： 2018.03
Cosmology in generalized Proca theories

Shinji Tsujikawa [Invited]

Ninth Aegean summer school- Einstein's theory of gravity and its modifications: From theory to observations (Sifnos Island, Greece)

Presentation date： 2017.09
Hairy black holes in vector-tensor theories

Shinji Tsujikawa, Lavinia Heisenberg, Ryotaro Kase, Masato Minamitsuji

4-th Korea-Japan joint workshop on dark energy at KMI (Nagoya)

Presentation date： 2017.08
Inflationaway gravitational waves in a generalized class of Horndeski theories

Shinji Tsujikawa [Invited]

International Symposium on Gravitational Waves, 2017 (北京, 中国)

Presentation date： 2017.05
Dark energy in vector-tensor theories

Shinji Tsujikawa [Invited]

CosKASI Conference 2017 (Daejeon, Korea)

Presentation date： 2017.04
Beyond generalized Proca理論における宇宙論

中村進太郎, 加瀬竜太郎, 辻川信二

日本物理学会 (大阪大学，大阪)

Presentation date： 2017.03
Cosmology in generalized Proca theories

Shinji Tsujikawa [Invited]

Testing Gravity 2017 Conference (バンクーバー (カナダ))

Presentation date： 2017.01
Cosmology in generalized Proca theories

Shinji Tsujikawa [Invited]

4th International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Asymmetry (Hsinchu, Taiwan)

Presentation date： 2016.12
Theories of modified gravity

Shinji Tsujikawa [Invited]

CosPA 2016 (シドニー，シドニー大学)

Presentation date： 2016.11
Dark energy and modified gravity

Shinji Tsujikawa [Invited]

Hanoi workshop on general relativity and cosmology (Hanoi)

Presentation date： 2016.10
Cosmology in generalized Proca theories

Shinji Tsujikawa [Invited]

Varying Constants and Fundamental Cosmology – VARCOSMOFUN’16 (Szczecin)

Presentation date： 2016.09
Classification of modified gravity models

Shinji Tsujikawa [Invited]

CosKASI-ICG-NAOC-YITP Workshop 2016 (大田，韓国)

Presentation date： 2016.09
Screening fifth forces in Generalized Proca Theories

Shinji Tsujikawa [Invited]

CosKASI-ICG-NAOC-YITP Workshop 2016 (大田，韓国)

Presentation date： 2016.09
Cosmology in generalized Proca theories

Shinji Tsujikawa [Invited]

IF-YITP GR+HEP+Cosmo International Symposium VI (Phitsanulok, Thailand)

Presentation date： 2016.08
Current status of dark energy and beyond

Shinji Tsujikawa [Invited]

PASCOS 2016: 22nd International Symposium on Particles, Strings and Cosmology (Quy Nhon, Vietnam)

Presentation date： 2016.07
Cosmology in generalized Proca theories

Shinji Tsujikawa, Antonio De Felice, Lavinia Heisenberg, Ryotaro Kase, Shinji Mukohyama, Yingli Zhang

3rd Korea-Japan Workshop on Dark Energy (大田 (韓国))

Presentation date： 2016.04
スペース重力波アンテナDECIGO計画

安東正樹, 辻川信二

日本物理学会 (仙台，東北学院大学)

Presentation date： 2016.03
Cosmology with a successful Vainshtein screening in theories beyond Horndeski

Ryotaro Kase, Shinji Tsujikawa, Antonio De Felice

日本物理学会 (仙台，東北学院大学)

Presentation date： 2016.03
Inflationary gravitational waves in the effective field theory of modified gravity

Shinji Tsujikawa [Invited]

Second LeCosPA International Symposium (台北 (台湾))

Presentation date： 2015.12
Current status of dark energy and beyond

Shinji Tsujikawa [Invited]

NCTS Annual Theory Meeting 2015: Particles, Cosmology, and Strings (新竹, 台湾)

Presentation date： 2015.12
ダークエネルギーとダークマター

辻川信二 [Invited]

一般相対論誕生100年記念講演会 (早稲田大学)

Presentation date： 2015.11
Effective field theory approach to modified gravity with applications to inflation and dark energy

Shinji Tsujikawa [Invited]

Early Universe, Cosmology and Fundamental Physics (北京 (中国))

Presentation date： 2015.09
Effective field theory approach to modified gravity with applications to inflation and dark energy

Shinji Tsujikawa [Invited]

Hot Topics in General Relativity and Gravitation (Quy Nhon, Vietnam)

Presentation date： 2015.08
Possibility of realizing weak gravity in red-shift space distortions

Shinji Tsujikawa

2-nd APCTP-TUS workshop on Dark Energy (東京理科大学)

Presentation date： 2015.08
Effective field theory of cosmological perturbations with application to dark energy

Shinji Tsujikawa [Invited]

Fourteenth Marcel Grossmann Meeting (Rome, Italy)

Presentation date： 2015.07
Effective field theory approach to modified gravity with applications to inflation and dark energy

Shinji Tsujikawa [Invited]

Annual Meeting of the Chinese Physical Society, Division of Gravitation and Relativistic Astrophysics (杭州 (中国))

Presentation date： 2015.06
Theories beyond General Relativity

Shinji Tsujikawa [Invited]

JERTE Advanced Relativity Workshop (Jerte, Spain)

Presentation date： 2015.03
Disformal invariance of cosmological perturbations in a generalized class of Horndeski theories

Shinji Tsujikawa [Invited]

Testing Gravity 2015 Workshop (バンクーバー，SFU Harbour Center)

Presentation date： 2015.01
宇宙論の最近のトピックス–インフレーション, 宇宙背景輻射, ダークエネルギー

辻川信二 [Invited]

第 37 回素粒子論グループ四国セミナー (新居浜高専)

Presentation date： 2014.12
暗黒エネルギーと修正重力理論

Shinji Tsujikawa [Invited]

第４回日大理工・益川塾連携素粒子物理学シンポジウム (京都)

Presentation date： 2014.11
A unified description of modified gravitational theories

Shinji Tsujikawa [Invited]

2-nd i-Link Workshop Macro-from-Micro: Quantum Gravity and Cosmology (CSIC (マドリード))

Presentation date： 2014.09
The effective field theory of modified gravity and the Horndeski theory

Shinji Tsujikawa [Invited]

Quantum Cosmology (Bad Honnef, Germany)

Presentation date： 2014.07
Effective field theory of modified gravity with two scalar fields: dark energy and dark matter

Shinji Tsujikawa [Invited]

1st APCTP-TUS workshop on Dark Energy (韓国，浦項)

Presentation date： 2014.06
暗黒エネルギーと修正重力理論

辻川信二 [Invited]

卓越した大学院拠点形成支援事業シンポジウム (東京，早稲田大学)

Presentation date： 2013.12
Discrimination between dark energy models from observations

Shinji Tsujikawa [Invited]

1st APCTP-NBIA joint workshop on Cosmology and Astroparticle Physics (Pohang, Korea)

Presentation date： 2013.10
Cosmological Perturbations in the Most General Scalar-Tensor Theories

Shinji Tsujikawa [Invited]

Seventh Aegean summer school, Beyond Einstein's theory of gravity (Paros, Greece)

Presentation date： 2013.09
Planck constraints on single-field inflation

Shinji Tsujikawa [Invited]

1-st i-Link Workshop Macro-from-Micro: Quantum Gravity and Cosmology (Madrid, Spain)

Presentation date： 2013.06
Cosmological perturbations in the most general scalar-tensor theories and their applications to dark energy

Shinji Tsujikawa [Invited]

The 8th Annual Conference of the Thai Physics Society Siam Physics Congress (SPC2013) (Chiangmai, Thailand)

Presentation date： 2013.03
Inflationary non-Gaussianities in the most general scalar-tensor theories

Shinji Tsujikawa, Antonio De Felice [Invited]

Kavli IPMU focus week on Gravity and Lorentz violations (Kavli IPMU, 柏)

Presentation date： 2013.02
Testing for dark energy models from distance measurements and redshift space distortions

Shinji Tsujikawa [Invited]

Thai-Japanese workshop (パタヤ，タイ)

Presentation date： 2012.12
Constraints on dark energy models from recent observations

Shinji Tsujikawa [Invited]

PPC2012 (Seoul, KIAS)

Presentation date： 2012.11
Discrimination between dark energy models from recent observations

Shinji Tsujikawa [Invited]

Multiverse and Fundamental Cosmology (Szczecin)

Presentation date： 2012.09
Potential-driven Galileon inflation

大橋純子, 辻川信二

日本物理学会 (京都)

Presentation date： 2012.09
スペース重力波アンテナDECIGO計画(38)：DECIGO/DPF

安東正樹, 辻川信二

日本物理学会 (京都)

Presentation date： 2012.09
Discrimination between dark energy models from recent observations

Shinji Tsujikawa [Invited]

Brazilian National Meeting on Particles and Fields (Passa Quartro, Brazil)

Presentation date： 2012.08
Discrimination between Theoretical Models of Dark Energy from Observations

Shinji Tsujikawa [Invited]

ICFPC 2012 (威海 (中国))

Presentation date： 2012.08
プランクによるインフレーションモデルの選別

Shinji Tsujikawa [Invited]

「背景放射で拓く宇宙創成の物理－インフレーションからダークエイジまで－」シンポジウム２０１２ (高エネルギー加速器研究機構 (つくば))

Presentation date： 2012.07
Vainshtein Mechanism With a Generalized Galileon Term

Antonio De Felice, Ryotaro Kase, Shinji Tsujikawa

Thirteenth Marcel Grossmann Meeting (ストックホルム・ストックホルム大学)

Presentation date： 2012.07
The Viability of Potential-driven Galileon Inflation

Junko Ohashi, Shinji Tsujikawa

Thirteenth Marcel Grossmann Meeting (ストックホルム・ストックホルム大学)

Presentation date： 2012.07
Selection of dark energy models from recent observations

Shinji Tsujikawa [Invited]

13-th Marcel Grossmann Meeting (ストックホルム (スウェーデン))

Presentation date： 2012.07
スカラーテンソル理論におけるヴァインシュタイン機構

加瀬竜太郎, Antonio De Felice, 辻川信二

日本物理学会 (西宮市，関西学院大学)

Presentation date： 2012.03
最も一般的なスカラーテンソル理論における密度揺らぎの進化と，暗黒エネルギー模型への応用

辻川信二, Antonio De Felice, 小林努

日本物理学会 (西宮市，関西学院大学)

Presentation date： 2012.03
スペース重力波アンテナDECIGO計画(36)：DECIGO/DPF

安東正樹, 辻川信二

日本物理学会 (西宮市，関西学院大学)

Presentation date： 2012.03
ダークエネルギーの理論模型と観測からの選別

Shinji Tsujikawa [Invited]

第五回超弦理論と宇宙研究会 (大分県別府市)

Presentation date： 2012.02
Dark energy in the most general scalar-tensor theories with second-order field equations

Shinji Tsujikawa [Invited]

The Dark Universe Conference (Heidelberg, Germany)

Presentation date： 2011.10
Observational status and models of dark energy

Shinji Tsujikawa [Invited]

Sixth Aegean summer school: Quantum gravity and quantum cosmology (Island of Naxos, Greece)

Presentation date： 2011.09
Inflation in modified gravitational theories

Shinji Tsujikawa, Antonio De Felice, Joseph Ellistion, Reza Tavakol

Summer Institute 2011 (宇宙・素粒子論) (富士吉田市, 富士Calm)

Presentation date： 2011.08
Dynamics of Dark Energy

Shinji Tsujikawa [Invited]

24-th Spring School on Particles and Fields (Hsinchu, Taiwan)

Presentation date： 2011.04
スペース重力波アンテナDECIGO計画(30)：設計・計画

川村静児, 辻川信二

日本物理学会 (新潟)

Presentation date： 2011.03
ガリレオン宇宙論における密度ゆらぎの進化

Antonio De Felice, 加瀬竜太郎, 辻川信二

日本物理学会 (新潟)

Presentation date： 2011.03
Observational constraints on assisted k-inflation

大橋純子, 辻川信二

日本物理学会 (新潟)

Presentation date： 2011.03
Galileon cosmology

Shinji Tsujikawa [Invited]

Indo-Japan workshop on cosmology (Delhi, India)

Presentation date： 2011.01
Galileon cosmology

Shinji Tsujikawa, Antonio De Felice, Savvas Nesseris [Invited]

Workshop on Beyond Standard Models and the Dark Sides of Our Universe (上海，中国)

Presentation date： 2010.11
Cosmology of a Galileon field

Shinji Tsujikawa, Antonio De Felice, Savvas Nesseris [Invited]

Extra-Dimension Probe by Cosmophysics (高エネルギー加速器研究機構，つくば)

Presentation date： 2010.11
Density perturbations in general modified gravity models of dark energy

Shinji Tsujikawa [Invited]

QGC2010 NIMS-APCTP Joint International Workshop: String Theory and Cosmology (Daejeon (Korea))

Presentation date： 2010.10
Inflation and dark energy-theoretical progress over 20 years

Shinji Tsujikawa [Invited]

The 20th workshop on General Relativity and Gravitation in Japan (JGRG20) (京都，京都大学)

Presentation date： 2010.09
Dark energy and modified gravity

Shinji Tsujikawa [Invited]

Confronting theory with observations -A UniverseNet Cosmology Workshop (Copenhagen, Denmark)

Presentation date： 2010.08
Density perturbations in general modified gravity theories

Shinji Tsujikawa, Antonio De Felice, Shinji Mukohyama

YKIS2010 symposium (京都)

Presentation date： 2010.06
Probing signatures of modified gravity models of dark energy

Shinji Tsujikawa [Invited]

IEU-APCTP Workshop, Cosmology and Fundamental Physics (Seoul, Korea)

Presentation date： 2010.05
Dark energy and modifications of gravity

Shinji Tsujikawa [Invited]

APCTP-IEU Focus Program (Pohang, Seoul)

Presentation date： 2010.05
Dark energy and modifications of gravity

Shinji Tsujikawa [Invited]

JOINT COSMO (柏市, 東京大学宇宙線研究所)

Presentation date： 2010.04
スペース重力波アンテナDECIGO計画(24)：設計・計画

川村静児, 安東正樹, 瀬戸直樹, 辻川信二

日本物理学会 (岡山大学)

Presentation date： 2010.03
拡張された重力理論における熱力学

馬塲一晴, Chao-Qiang Geng, 辻川信二

日本物理学会 (岡山大学)

Presentation date： 2010.03
Assisted dark energy

大橋純子, 辻川信二

日本物理学会 (岡山大学)

Presentation date： 2010.03
Recent status of dark energy

Shinji Tsujikawa [Invited]

Indo-Japan workshop on gravitation and cosmology (デリー，インド)

Presentation date： 2009.12
Assisted dark energy

Junko Ohashi, Shinji Tsujikawa

The Nineteenth Workshop on General Relativity and Gravitation (立教大学，東京)

Presentation date： 2009.11
Equilibrium description of thermodynamics in modified gravitational theories

Kazuharu Bamba, Chao-Qiang Geng, Shinji Tsujikawa

The Nineteenth Workshop on General Relativity and Gravitation (立教大学，東京)

Presentation date： 2009.11
Recent status of dark energy

Shinji Tsujikawa [Invited]

International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Asymmetry (Hsinchu, Taiwan)

Presentation date： 2009.11
Dark energy and modified gravity

Shinji Tsujikawa [Invited]

Λ-LTB Cosmology (高エネルギー加速器研究機構，つくば)

Presentation date： 2009.10
Dark energy and modified gravity

Shinji Tsujikawa [Invited]

NIMS-APCTP Joint International workshop "String Theory and Cosmology - Quantum Gravity Dark Energy and Dark Matter" (Daejeon, Korea)

Presentation date： 2009.09
Dark energyの理論的な模型と観測からの制限

辻川信二 [Invited]

第39回天文天体物理若手夏の学校 (群馬県・草津町)

Presentation date： 2009.07
Matter density perturbations in modified gravity models of dark energy

Shinji Tsujikawa

IPMU International Conference dark energy: lighting up the darkness! (柏, 東京大学数物連携宇宙研究機構)

Presentation date： 2009.06
スペース重力波アンテナDECIGO計画

川村静児, 安東正樹, 瀬戸直樹, 辻川信二

日本物理学会 (東京・立教大)

Presentation date： 2009.03
一般的な暗黒エネルギー模型における物質の密度揺らぎ

辻川信二

日本物理学会 (東京・立教大)

Presentation date： 2009.03
Scalar-tensor dark energy models and their observational implications.

Shinji Tsujikawa [Invited]

India-Japan workshop on cosmology (Delhi, India)

Presentation date： 2008.12
Overview lecture of modified gravity

Shinji Tsujikawa [Invited]

TRR33 Winter School (Passo del Tonale, Italy)

Presentation date： 2008.12
Revisting chameleon gravity: thin-shells and no-shells with appropriate boundary conditions

Takashi Tamaki, Shinji Tsujikawa

RESCEU Symposium on Astroparticle Physics and Cosmology (The University of Tokyo, Japan)

Presentation date： 2008.11
Scalar-Tensor Models of Dark Energy and Their Observational Signatures

Shinji Tsujikawa [Invited]

Cosmology Workshop Montpellier08 (フランス，モンペリエ)

Presentation date： 2008.10
Dark energy and modified gravity

Shinji Tsujikawa [Invited]

Accelerators in the Universe (つくば)

Presentation date： 2008.03
f(R)重力理論に基づく暗黒エネルギー模型の宇宙論的な妥当性のための条件

Shinji Tsujikawa, Luca Amendola, Radouane Gannouji, David Polarski

日本物理学会 (北海道)

Presentation date： 2007.09
Conditions for the cosmological viability of f(R) dark energy models

Shinji Tsujikawa, Luca Amendola, Radouane Gannouji, David Polarski

Cosmo-2007 (ブライトン，英国)

Presentation date： 2007.08
スケーリング解を用いた暗黒エネルギー模型の妥当性の研究

Shinji Tsujikawa, Luca Amendola, Miguel Quartin, Iaov Waga

日本物理学会 (東京)

Presentation date： 2007.03
Current status of cosmic inflation

Shinji Tsujikawa [Invited]

24-th IAGRG Meeting (India, Delhi, University of Jamia Millia Islamia)

Presentation date： 2007.02
Challenges for scaling cosmologies

Shinji Tsujikawa, Luca Amendola, Miguel Quartin, Iaov Waga [Invited]

Cosmology Workshop Montpellier06 (モンペリエ, フランス)

Presentation date： 2006.11
Cosmological viability of f(R) dark energy models

Shinji Tsujikawa, Luca Amendola, David Polarski

日本物理学会 (奈良)

Presentation date： 2006.09
A unified analysis for cosmological scaling solutions and its application to dark energy

Shinji Tsujikawa, Federico Piazza, M. Sami

2-nd Sino-French Workshop on dark universe (北京, 中国)

Presentation date： 2006.08
Reconstruction of general scalar-field dark energy models

Shinji Tsujikawa

日本物理学会 (松山)

Presentation date： 2006.03
A unified analysis for cosmological scaling solutions and its application to dark energy

Shinji Tsujikawa, Federico Piazza, M. Sami

3-rd Aegean summer school (ヒオス島, ギリシャ)

Presentation date： 2005.09
Dark energy and cosmological solutions in second-order string gravity

Shinji Tsujikawa, Gianlulca Calcagni, M. Sami

日本物理学会 (大阪)

Presentation date： 2005.09
Cosmology from higher-order string corrections

Shinji Tsujikawa [Invited]

Pomeranian Workshop in Fundamental Cosmology (Poland, University of Szczecin)

Presentation date： 2005.09
Dark energy and cosmological solutions in second-order string gravity

Shinji Tsujikawa, Gianluca Calcagni, M. Sami

Cosmo-2005 (ボン, ドイツ)

Presentation date： 2005.08
Inflation and cosmological perturbations

Shinji Tsujikawa [Invited]

The 3rd Thai Physics and the Universe Symposium (ピサニュロック, タイ)

Presentation date： 2005.08
Unified analysis for cosmological scaling solutions and its application to dark energy

Shinji Tsujikawa, M. Sami

YKIS-05 (京都)

Presentation date： 2005.06
宇宙論的なスケーリング解が満たすラグランジアンとその暗黒エネルギーのモデルへの応用

Shinji Tsujikawa, Federico Piazza, M. Sami

日本物理学会 (野田)

Presentation date： 2005.03
Inflationary models and observational constraints

Shinji Tsujikawa

Workshop on strings and cosmology (プネ, インド)

Presentation date： 2004.10
Inflationary models and observational constraints

Shinji Tsujikawa

Workshop on strings and cosmology (India, Pune, IUCAA)

Presentation date： 2004.10
インフレーションモデルの最近の観測からの制限

Shinji Tsujikawa

日本物理学会 (高知)

Presentation date： 2004.09
Observational constraints on inflation and its implication for particle physics

Shinji Tsujikawa

Braneworlds and quantum cosmology (プネ, インド)

Presentation date： 2004.01
Construction of nonsingular cosmological solutions in string theories

Shinji Tsujikawa

COSMO-2003 (アンブルサイド, 英国)

Presentation date： 2003.08
Construction of Nonsingular Pre-Big-Bang and Ekpyrotic Cosmologies and the Resulting Density Perturbations

Shinji Tsujikawa, Robert Brandenberger, Fabio Finelli

The Second Tah Poe conference on Cosmology (ピサニュロック, タイ)

Presentation date： 2003.04
Introductory review of cosmic inflation

Shinji Tsujikawa [Invited]

The Second Tah Poe School on Cosmology (Thailand・Naresuan University)

Presentation date： 2003.04
Power spectra and consistency relations in double inflation

Shinji Tsujikawa, David Parkinson, Bruce A. Bassett

日本物理学会 (仙台)

Presentation date： 2003.03
Power spectra and consistency relations in double inflation

Shinji Tsujikawa, David Parkinson, Bruce A. Bassett

Texas Symposium (フイレンチェ, イタリア)

Presentation date： 2002.12
Construction of nonsingular Pre-Big-Bang and Ekpyrotic cosmologies and the cosmological density perturbations

Shinji Tsujikawa, Robert Brandenberger, Fabio Finelli

日本物理学会 (東京)

Presentation date： 2002.09
時空の揺らぎによる粒子生成

Shinji Tsujikawa, Bruce A. Bassett, Marco Peloso, Lorenzo Sorbo

日本物理学会 (草津 (滋賀))

Presentation date： 2002.03
Parametric resonanceと初期ブラックホール形成

Shinji Tsujikawa [Invited]

重力波研究の発展と将来 (京都)

Presentation date： 2002.02
Gravitational particle production from metric perturbations

Shinji Tsujikawa, Bruce A. Bassett, Marco Peloso, Lorenzo Sorbo

一般相対論と重力研究会 (東京)

Presentation date： 2002.01
Gravitational particle production from metric perturbations

Shinji Tsujikawa, Bruce A. Bassett, Marco Peloso, Lorenzo Sorbo

The 5th RESCEU International Symposium (Tokyo)

Presentation date： 2001.11
一般化されたアインシュタイン理論に基づくインフレーションでの密度揺らぎ

Shinji Tsujikawa, Alexei A. Starobinsky, Jun'ichi Yokoyama

日本物理学会 (沖縄)

Presentation date： 2001.09
Cosmological perturbations from multi-field inflation in generalized Einstein theories

Shinji Tsujikawa, Alexei A. Starobinsky, Jun'ichi Yokoyama

GR-16 (ダーバン, 南アフリカ)

Presentation date： 2001.07
Inflation and preheating with extra dimensions

Shinji Tsujikawa

日本物理学会 (東京)

Presentation date： 2001.03
Metric preheating with a nonminimally coupled inflaton field

Shinji Tsujikawa, Bruce A. Bassett

日本物理学会 (新潟)

Presentation date： 2000.09
Multi-field fermionic preheating

Shinji Tsujikawa, Bruce A. Bassett, Fermin Viniegra

一般相対論と重力研究会 (大阪)

Presentation date： 2000.09
Multi-field fermionic preheating

Shinji Tsujikawa, Bruce A. Bassett, Fermin Viniegra

COSMO-2000 (済州島, 韓国)

Presentation date： 2000.09
Preheating of non-minimally coupled scalar fields

Shinji Tsujikawa, Kei-ichi Maeda, Takashi Torii

The 9th Marcel Grossmann meeting (Rome, Italy)

Presentation date： 2000.07
Spinodal effect in the natural inflation model

Shinji Tsujikawa, Takashi Torii

日本物理学会 (大阪)

Presentation date： 2000.03
Neutrino oscillations in strong gravitational fields

Shinji Tsujikawa, Jun'ichiro Koga, Kei-ichi Maeda

一般相対論と重力研究会 (広島)

Presentation date： 1999.11
Preheating of the nonminimally coupled inflaton field

Shinji Tsujikawa, Kei-ichi Maeda, Takashi Torii

The 4th RESCEU International Symposium (Tokyo)

Presentation date： 1999.11
Preheating of the nonminimally coupled inflaton field

Shinji Tsujikawa, Kei-ichi Maeda, Takashi Torii

日本物理学会 (島根)

Presentation date： 1999.10
Preheating with nonminimally coupled scalar fields via higher-curvature inflation models

Shinji Tsujikawa, Kei-ichi Maeda, Takashi Torii

日本物理学会 (広島)

Presentation date： 1999.03
Resonant particle production with nonminimally coupled scalar fields in reheating process

Shinji Tsujikawa, Kei-ichi Maeda, Takashi Torii

日本物理学会 (秋田)

Presentation date： 1998.10

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Research Projects

重力理論と新しい場の物理の多角的な検証

日本学術振興会科学研究費助成事業

Project Year :

2022.04

-

2026.03

辻川信二
Formation of primordial black holes after inflation in modified gravity and supergravity

日本学術振興会科学研究費助成事業

Project Year :

2022.04

-

2025.03

Sergei V.Ketov, 藤田裕, 辻川信二
Testing quantum gravity with cosmological perturbations

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2020.11

-

2023.03
多様な観測データによる一般相対論の拡張理論の検証

日本学術振興会科学研究費助成事業

Project Year :

2019.04

-

2023.03

辻川信二

　View Summary

本年度は，ダークエネルギーがダークマターと結合している具体的な理論的な模型の構築を行った．特に，両者が4元速度の差を通じて相互作用している模型をラグランジアンレベルで具体的に構築した．この模型は，宇宙初期にダークエネルギーが暗黒輻射として振るまい，さらに宇宙後期にはダークマターの揺らぎの成長率を抑制することが可能な模型であり，標準的な宇宙項模型でのハッブル定数および物質揺らぎの振幅の観測的な不一致問題を改善することが予測される．実際に，宇宙背景輻射，Ia型超新星，バリオン音響振動などの観測データを用いた統計解析を行い，これらの不一致問題が緩和されることを示した．さらに我々の解析結果は，ダークエネルギーとダークマターが結合している可能性も示唆しており，これは宇宙の暗黒成分の起源に迫る上で極めて重要な意味を持つ．
さらに，スカラー場が重力と結合している一般的な枠組みであるホルンデスキ理論において，スカラー化したブラックホールや中性子星の安定性を議論するために，静的・球対称の背景時空において奇パリティと偶パリティの摂動に関する一般的な定式化を行なった．この取り扱いは，摂動に関するゲージを固定しない極めて一般的な解析であり，さらにゴーストやラプラシアン不安定性が存在しない条件を一般的に明らかにしたものである．この条件を今までに知られていたブラックホール解に適用することで，いくつかの解が不安定性から棄却されることを示した．
また，スカラー場と電磁場が結合した系において，帯電した星の電荷が大きくなると星に不安定性が生じ，自発的なスカラー化が起こることで星がより安定な状態に遷移することを示した．以上の成果は，全てPhysical Review D，Physics Letters Bなどの学術論文に出版されている．
Theoretical modeling of dark energy and its observational verification

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2015.06

-

2020.03

Sugiyama Naoshi

　View Summary

Observational Constraints on dark energy models were obtained using the latest astronomical observational data, mainly from Planck. Various theoretically motivated dark energy models were proposed, and parameter regions of the theory that satisfy current observations were obtained. We developed a cosmological perturbation theory in models with dark energy and dark matter interactions and found that such models slow down the formation of large scale structure of the universe. We examined the effect of density fluctuations of dark energy on the number density and size of voids formed in the large-scale structure of the universe, and showed that the Alcock-Pacynski test allows unbiased constraints on the energy density of dark energy and the equation of state.
Theoretical and observational probes for theories beyond General Relativity

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2016.04

-

2019.03

TSUJIKAWA SHINJI

　View Summary

It is observationally known that the two stages of cosmic acceleration occurred in the early and late Universes. To address these fundamental problems, we constructed theoretically viable models of cosmic acceleration in general relativity and extended theories of gravity. In particular, we successfully constructed dark energy models based on scalar/vector fields and studied their observational signatures in detail. By using the new data of gravitational waves obtained in 2017, we distinguished between theoretical models consistent with observations. We showed that dark energy models in vector-tensor theories exhibit a better fit to the data compared to the standard cosmological constant. Our works played important roles to approach the origin of cosmic acceleration.
Modified Supergravity Models of Cosmological Inflation and Particle Production in Early Universe

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2014.04

-

2019.03

Ketov Sergei V., Maeda Keiichi, Tsujikawa Shinji, Hamaguchi Koichi

　View Summary

The purpose of our research is to understand the evolution of the Universe, and the origin of elementary particles. This is related to the more specific problems such as (i) what causes the accelerated expansion of the Universe?, (ii) what is the reason for keeping the galaxies together?, and (iii) what is the mechanism of the structure formation in the early Universe? These problems are called dark energy, dark matter, and inflation, respectively. The current scientific knowledge about gravity and elementary particles is not enough to address these problems, so that more advanced theories should be developed. Our approach is based on the supergravity theory that unifies gravity with other forces and relates particles of different spin and statistics. We succeeded in constructing the new models of supergravity, which are consistent with all observations and have the specific mechanisms of inflation and dark energy, together with a suitable elementary particle for dark matter.
一般相対論を拡張した理論の構築とその観測的検証

日本学術振興会科学研究費助成事業

Project Year :

2015.11

-

2018.03

辻川信二, ARRAUT GUERRERO IVAN

　View Summary

当該年度は，暗黒エネルギーの起源を解明するために，基礎方程式が2階微分に保たれるホルンデスキー理論とそれを拡張した理論において，太陽系のような局所領域での重力結合の強さと宇宙進化について調べた。研究代表者らは，そのような理論において，模型によっては局所天体の中心において曲率の発散が起こることを示し，そのような発散が起こらないための条件について明らかにした。さらに，宇宙の構造形成に関連する揺らぎの成長率が，観測と合うレベルで小さくできることを示した。このような模型において，背景時空の宇宙進化および宇宙の局所領域での第5の力の強さについて詳細に調べ，観測と矛盾しない模型の構築を行い，さらに有効なパラメータ領域に制限を与えた．
上記の研究に加えて研究代表者らは，質量をもつベクトル場に基づく極めて一般的な拡張重力理論において，宇宙の局所領域での第5の力の伝搬機構と宇宙進化について詳細に調べた。その結果として，宇宙が加速膨張する解の存在を見出し，しかも一般的に収束解になっていることを示した。それらに加えて，理論にゴーストや不安定性が現れない条件を導出し，暗黒エネルギー模型として有効であるための条件について明らかにした。さらに，太陽系のような宇宙の局所領域において，ベクトル場のもつ自己相互作用によって，模型が重力実験と整合的であることを示した。さらに，重力子が質量をもつmassive gravity理論におけるヒッグス機構に関して調べた。
宇宙物理学，相対論

Project Year :

2008

-

2018

　View Summary

近年の観測技術の進歩に伴い，宇宙論および重力理論に関する研究は急速な進展を見せている．本研究室では，一般相対論や素粒子理論を用いた理論的な予言と最新の観測データとの比較を行い，宇宙の初期から現在に至る宇宙の進化について明らかにしようとしている．
Cosmology, Relativity

Project Year :

2008

-

2018

　View Summary

The research area of cosmology and general relativity has rapidly developed with the improvement of observational techniques. We try to clarify the evolution of Universe from the beginning to the present by comparing theoretical predictions from general relativity and particle physics with recent observational data.
Probing theoretical models of dark energy from latest observations

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2012.04

-

2016.03

TSUJIKAWA Shinji

　View Summary

From the observations of supernovae it is known that the present Universe is accelerating, but the origin of cosmic acceleration has not been identified yet. To reveal the origin of dark energy, I constructed a general theoretical framework for dealing with dark energy models in modified gravitational theories. In such a general scheme I studied the cosmic expansion history, the evolution of density perturbations, and the gravitational couplings in the solar system, which is vey useful to distinguish between theoretical models of dark energy. In addition, we placed constraints on each dark energy model from the observations of supernovae, cosmic microwave background, and large-scale structures.
research on cosmological nonlinear and non-perturbative gravitational phenomena

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2009.04

-

2015.03

SASAKI Misao, TANAKA Takahiro, SHIROMIZU Tetsuya, SODA Jiro, MUKOHYAMA Shinji, MATSUBARA Takahiko, TAKAHASHI Fuminobu, CHIBA Takeshi, TSUJIKAWA Shinji, ISHIHARA Hideki, YAMAMOTO Kazuhiro, YAMAGUCHI Masahide

　View Summary

It is believed that the universe has undergone a stage of accelerated expansion, an inflationary stage, right after the birth, and all the fluctuations that are responsible for the structure of the universe today were generated during this stage. One of the most important issues in cosmology is to understand how these fluctuations have evolved to the large scale structure of the universe such as galaxies through nonlinear and non-perturbative gravitational phenomena. In this project, we have systematically investigated various types of fluctuations, from microscopic quantum fluctuations to macroscopic fluctuations of spacetime, and obtained many world top-class results. These results form an important basis for the future direction of research in cosmology.
Quest for the ultimate theory on the basis of direct observations of the early evolution of the universe

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2009.07

-

2014.03

KODAMA Hideo, KAWASAKI Masahiro, YOKOYAMA Jun'ichi, SODA Jiro, TSUJIKAWA Shinji, MUKOHYAMA Shinji, NAKAYAMA Kazunori, KITAZAWA Yoshihisa, CHIBA Takeshi, SHIROMIZU Tetsuya, TANAKA Takahiro, KOHRI Kazunori, TAKAHASHI Fuminobu, NOZZWA Masato, NAKAYAMA Kazunori

　View Summary

In this project, we have pushed forward investigations from the two different directions, the phenomomenology of the universe focused on cosmological fluctuations and the construction of universe models based on unified theories including gravity, and published more than 300 papers. The most significant resutls are the construction of the most general inflation theory with a single driving scalar field and the comparison of its predictions with observations, the construction of a consistent anisotropic inflation model and the derivation of its detailed observational predictions, the construction of a variety of large field inflation models on the basis of 4D supergravity unified theories, derivation of constraints on elementary particle theory on the basis of investigations of axion cosmology by 3D numerical simulations, clarification of the IR divergence problem in quantum correstions to inflation, and systematic studies of various modified gravity theories.
暗黒エネルギーと修正重力理論

日本学術振興会科学研究費助成事業

Project Year :

2010

-

2012

辻川信二, GANNOUJI Radouane

　View Summary

修正重力理論では,物質に働く重力の強さが大スケールで変更を受け,密度揺らぎの進化が異なるために,宇宙の大規模構造や宇宙背景輻射などの観測量に影響を与える.研究代表者の辻川と研究分担者のGannouji氏は,f(R)理論,Galileon理論,Weyl理論における宇宙進化について詳細に調べ,それらの模型が宇宙論的に有効である条件について明らかにした.さらに,ゴーストや不安定性の問題を回避できる一般的な修正重力理論において,物質密度揺らぎと重力ポテンシャルが従う式を導出した.それに加えて,赤方偏移空間での銀河分布のスペクトルの最新の観測を用いて,f(R)理論とGalileon理論に基づく暗黒エネルギー模型の有効なパラメータ領域について明らかにした。これらの修正重力理論では,物質揺らぎの成長率がLCDM模型と異なることから,観測的に模型の選別ができることを示した.
また修正重力理論では,宇宙の局所領域で一般相対論的な特徴を回復する必要があるが,そのような機構の一つとして,ヴァインシュタイン機構がある.我々は,Galileon場が小さな質量を持つ場合に,どのようにヴァインシュタイン機構が働くかを詳細に調べた.さらに,ガウスボンネ項が存在する高次元理論を4次元有効理論に落としたときに現れるスカラー自由度によって,ヴァインシュタイン機構が働き,第5の力の伝搬が妨げられることを示した.
上記の研究成果は,ストックホルムで開かれた会議において,Gannouji氏と辻川が発表し,研究成果の公表につとめた.また,これらの成果は,すでにPhysics Letters B誌やJCAP誌に掲載されている.
修正重力理論, 素粒子物理に基づく暗黒エネルギーの起源の探究

日本学術振興会科学研究費助成事業

Project Year :

2009

-

2011

辻川信二, DEFELICE Antonio, DE FELICE Antonio, DE FELICE Antonio

　View Summary

本年度は,ほとんどの暗黒エネルギー模型を含むような一般的なスカラーテンソル理論における,宇宙論的密度揺らぎの進化と模型の有効性の条件を明らかにする研究を主に行った.特に,宇宙の大規模構造や重力レンズの観測と関連する物質の密度揺らぎに関して,その成長率を決める実効的な重力結合の大きさを一般的に導出した.さらに,重力ポテンシャルの進化を表す式も導きだし,これは宇宙背景輻射の観測と直接関係する重要な結果である.また,一般的なスカラーテンソル理論においてゴーストや不安定性を避ける条件を求めることで,有効な暗黒エネルギー模型の構築に重要な寄与を与えたと考えられる.特に,ガリレオンと呼ばれるスカラー場を拡張した新たな暗黒エネルギー模型を提唱し,理論的に矛盾のないパラメータ領域を明らかにした.さらに,この新たな模型でトラッカーと呼ばれるアトラクター解の存在を示し,これは最終的に加速膨張へとつながる解である.このトラッカー解に関して,超新星,宇宙背景輻射,バリオン音響振動の最新の観測から,有効なパラメータ領域に制限を与えた,さらに,物質密度揺らぎと宇宙背景輻射の温度揺らぎとの相関から,模型にどのような制限がつくかについての研究も行った.
これらの研究に加えて,宇宙の局所領域において一般相対論を回復する機構を,スカラーテンソル理論において調べた。特に,理論が一般相対論的な特徴を回復するような半径(ヴァインシュタイン半径)を一般的に導出した.このヴァインシュタイン機構が有効に働くための条件から,修正重力理論のラグランジアンに制限を与えた.以上のように,暗黒エネルギーの宇宙論的なダイナミックスと宇宙の局所領域の振る舞いから,暗黒エネルギーの模型の選別を行い,将来の観測からの模型への制限に重要な寄与を与えたと考えられる.
Construction of theoretical models of dark energy and their observational constraints

Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research

Project Year :

2008

-

2011

TSUJIKAWA Shinji

　View Summary

Observations such as supernova type Ia suggest that about 70% of the energy density of the Universe today consists of dark energy responsible for cosmic acceleration. The development of both theoretical and observational sides is required to approach the origin of dark energy. From the theoretical side I discriminated between many models of dark energy by studying the background cosmological dynamics, the evolution of density perturbations, and local gravity constraints. Moreover we placed constraints on theoretical models of dark energy from a number of independent observational data.
インフレーションおよび暗黒エネルギーの模型の理論的な構築と最新の観測からの制限

日本学術振興会科学研究費助成事業

Project Year :

2005

-

2007

辻川信二

　View Summary

本年度は,一般相対論を拡張したシナリオにおける暗黒エネルギー模型の構築と,それに対する観測からの制限をつける研究を主に行った.これは,暗黒エネルギーの起源が宇宙項であるかそれとも重力理論の変更によるものであるかを明らかにする上で,極めて重要である.特に我々は,そのような模型が宇宙論的に有効である条件を一般的に明らかにし,この解析方法はこの1年の間に多くの研究者により用いられた.また,そのような模型に対する局所重力実験からの制限も考慮し,有効な模型の構築を行った.さらに,宇宙背景輻射の温度揺らぎや宇宙の大規模構造の物質揺らぎと理論の予言を比較することにより,模型に対する制限をつけた.
また,一般相対論を変更したシナリオのほとんど全てを含むような一般的な系において,物質の密度揺らぎが従う式をある近似のもとで導き出した.この結果は,将来の重力レンズやライマンアルファ線の観測から暗黒エネルギーの性質に制限をつける上で,極めて重要な役割を果たすと期待される.
上記は主に暗黒エネルギーに関する研究であるが,もう1つの研究課題であるインフレーション宇宙論に関しても,超弦理論を用いた妥当な模型の構築を行った.我々は特に,インフレーションを起こす場と,余剰次元の大きさに相当する場が共存する系における加速膨脹の機構について明らかにし,余剰次元による寄与が,加速膨脹の程度を評価する上で本質的に重要な役割を果すことを示した.さらに,それにより生成される密度揺らぎの大きさとスペクトラムを理論的に計算し,宇宙背景輻射の最新の観測から模型に制限をつけた.
宇宙初期のインフレーション理論に基づく宇宙進化の探究

日本学術振興会科学研究費助成事業

Project Year :

2001

-

2003

辻川信二

　View Summary

本年度からは、超重力理論に基づく密度揺らぎの計算、インフレーション理論に対する観測からの制限、超紐理論に基づく宇宙進化の解析等の研究を行った。特に、2つのスカラー場が存在する系で、断熱揺らぎと等曲率揺らぎのスペクトラム、2つの揺らぎの相関についての詳細な解析を行い、一般的に超重力理論に基づくインフレーションモデルにおいては、相関が非常に大きくなることを見いだした。この研究により、宇宙背景輻射の温度揺らぎに対する、等曲率揺らぎの存在の重要性が明らかにされた。また、非可換時空の理論に基づくインフレーションモデルの構築を行い、宇宙背景輻射の観測データの情報を用いながら、モデルへの制限を行った。特に、観測的に示唆されているような大スケールでの密度揺らぎの振幅の衰退について、このモデルで説明可能であることを示した。また最近、ブレーン宇宙論に基づくインフレーションモデルに対する観測からの制限をつけることを試み、いくつかのモデルは観測的には好まれないことを示した。
また、宇宙が超紐の理想気体で満たされているような系での宇宙進化について解析的、数値的に調べ、3次元空間のみを大きくし、余剰次元を小さく保つようなモデルの構築を行った。さらにこのシナリオを拡張し、超紐理論の一般的な有効作用を用いた特異点のない宇宙モデルの考察を行い、宇宙が収縮から膨張に転じるような解を見いだした。特にそのような場合、無限の過去と未来において時空の曲率と超紐の結合定数を有限に保つことができることを示した。このことは、超紐理論に基づいて特異点のない解を構成する際に非常に重要な示唆を与えると期待される。

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Misc

19aSA-10 Effective field theory of modified gravity on the spherically symmetric background : leading order dynamics and the odd-type perturbations

Kase Ryotaro, Gergely Laszlo A., Tsujikawa Shinji

Meeting abstracts of the Physical Society of Japan 69 ( 2 ) 35 - 35 2014.08

CiNii
22pSN-5 Anisotropic non-Gaussianity from a two-form field

Ohashi Junko, Soda Jiro, Tsujikawa Shinji

Meeting abstracts of the Physical Society of Japan 68 ( 2 ) 114 - 114 2013.08

CiNii
26pBB-8 Vainshtein mechanism in the most general second-order scalar-tensor theories

Kase Ryotaro, Tsujikawa Shinji

Meeting abstracts of the Physical Society of Japan 68 ( 1 ) 119 - 119 2013.03

CiNii
Dark energy in the most general scalar-tensor theories and their observational constraints

Shinji Tsujikawa

MULTIVERSE AND FUNDAMENTAL COSMOLOGY: MULTICOSMOFUN '12 1514 118 - 127 2013

DOI
25pGH-12 Vainshtein mechanism in second-order scalar-tensor theories

Antonio De Felice, Kase Ryotaro, Tsujikawa Shinji

Meeting abstracts of the Physical Society of Japan 67 ( 1 ) 136 - 136 2012.03

CiNii
24pGJ-6 Space Gavitational-Wave Antenna DECIGO (36) : DECIGO/DPF

Ando Masaki

Meeting Abstracts of the Physical Society of Japan 67 ( 0 ) 126 - 126 2012

DOI CiNii
隠れた定数～暗黒エネルギー～

白水徹也, 辻川信二他

数理科学 ( 2011年7月 ) 17 - 24 2011.07
Cosmological Perturbations in General Modified Gravity Theories

Shinji Tsujikawa, Antonio De Felice, Shinji Mukohyama

PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT 190 ( 190 ) 188 - 196 2011

　View Summary

We derive the equations of linear cosmological perturbations for the general Lagrangian density f (R,phi,X)/2 + L-c, where R is a Ricci scalar, phi is a scalar field, and X = -partial derivative(mu)phi partial derivative(mu)phi/2 is a field kinetic energy. We take into account a nonlinear self-interaction term L-c = xi(phi)square phi(partial derivative(mu)phi partial derivative(mu)phi), which keeps the field equations at second order. Taking into account a scalar-field mass explicitly, the equations of matter density perturbations and gravitational potentials are obtained under a quasi-static approximation on sub-horizon scales. We also derive conditions for the avoidance of ghosts and Laplacian instabilities associated with propagation speeds.
Matter instabilities in general Gauss-Bonnet gravity

Antonio De Felice, David F. Mota, Shinji Tsujikawa

MODERN PHYSICS LETTERS A 25 ( 11 ) 885 - 889 2010.05
RECENT STATUS OF DARK ENERGY

Shinji Tsujikawa

MODERN PHYSICS LETTERS A 25 ( 11-12 ) 843 - 858 2010.04

　View Summary

We review a number of approaches that have been adopted to explain the origin of dark energy responsible for the late-time cosmic acceleration. This includes the cosmological constant and dynamical dark energy models such as quintessence, k-essence, Chaplygin gas, f(R) gravity, scalar-tensor theories, and braneworld models. We also discuss observational and local gravity constraints on those models and clarify which models are favored or ruled out in current observations.

DOI
23aBQ-6 Thermodynamics in extended gravitational theories

Bamba Kazuharu, Geng Chao-Qiang, Tsujikawa Shinji

Meeting abstracts of the Physical Society of Japan 65 ( 1 ) 129 - 129 2010.03

CiNii
Dark energy: Theory and observations

Luca Amendola, Shinji Tsujikawa

Dark Energy: Theory and Observations 1 - 491 2010.01

Other

DOI
ループ量子宇宙論

辻川信二, 小玉英雄

数理科学 ( 2009年10月 ) 80 - 86 2009.10
アインシュタイン方程式

辻川信二, 和達三樹

数理科学 ( 6月 ) 42 - 46 2009.06
DECIGO Pathfinder

Masaki Ando, Seiji Kawamura, Takashi Nakamura, Kimio Tsubono, Takahiro Tanaka, Ikkoh Funaki, Naoki Seto, Kenji Numata, Shuichia Sato, Kunihito Ioka, Nobuyuki Kanda, Takeshi Takashima, Kazuhiro Agatsuma, Tomotada Akutsu, Tomomi Akutsu, Koh-suke Aoyanagi, Koji Arai, Yuta Arase, Akito Araya, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Shogo Kamagasako, Nobuki Kawashima, Fumiko Kawazoe, Hiroyuki Kirihara, Naoko Kishimoto, Kenta Kiuche, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Noriyasu Nakagawa, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Akira Okutomi, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Hideyuki Tagoshi, Kakeru Takahashi, Keitaro Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Ryuichi Takahashi, Ryutaro Takahashi, Akiteru Takamori, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Mitsuru Tokuda, Masao Tokunari, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Ken-ichi Ueda, Masayoshi Utashima, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino

TAUP2007: TENTH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS 120 ( 032005 ) 1 - 5 2008

DOI
The Japanese Space Gravitational Wave Antenna; DECIGO

Seiji Kawamura, Masaki Ando, Takashi Nakamura, Kimio Tsubono, Takahiro Tanaka, Ikkoh Funaki, Naoki Seto, Kenji Numata, Shuichi Sato, Kunihito Ioka, Nobuyuki Kanda, Takeshi Takashima, Kazuhiro Agatsuma, Tomotada Akutsu, Tomomi Akutsu, Koh-suke Aoyanagi, Koji Arai, Yuta Arase, Akito Araya, Hideki Asada, Yoichi Aso, Takeshi Chiba, Toshikazu Ebisuzaki, Motohiro Enoki, Yoshiharu Eriguchi, Masa-Katsu Fujimoto, Ryuichi Fujita, Mitsuhiro Fukushima, Toshifumi Futamase, Katsuhiko Ganzu, Tomohiro Harada, Tatsuaki Hashimoto, Kazuhiro Hayama, Wataru Hikida, Yoshiaki Himemoto, Hisashi Hirabayashi, Takashi Hiramatsu, Feng-Lei Hong, Hideyuki Horisawa, Mizuhiko Hosokawa, Kiyotomo Ichiki, Takeshi Ikegami, Kaiki T. Inoue, Koji Ishidoshiro, Hideki Ishihara, Takehiko Ishikawa, Hideharu Ishizaki, Hiroyuki Ito, Yousuke Itoh, Shogo Kamagasako, Nobuki Kawashima, Fumiko Kawazoe, Hiroyuki Kirihara, Naoko Kishimoto, Kenta Kiuchi, Shiho Kobayashi, Kazunori Kohri, Hiroyuki Koizumi, Yasufumi Kojima, Keiko Kokeyama, Wataru Kokuyama, Kei Kotake, Yoshihide Kozai, Hideaki Kudoh, Hiroo Kunimori, Hitoshi Kuninaka, Kazuaki Kuroda, Kei-ichi Maeda, Hideo Matsuhara, Yasushi Mino, Osamu Miyakawa, Shinji Miyoki, Mutsuko Y. Morimoto, Tomoko Morioka, Toshiyuki Morisawa, Shigenori Moriwaki, Shinji Mukohyama, Mitsuru Musha, Shigeo Nagano, Isao Naito, Noriyasu Nakagawa, Kouji Nakamura, Hiroyuki Nakano, Kenichi Nakao, Shinichi Nakasuka, Yoshinori Nakayama, Erina Nishida, Kazutaka Nishiyama, Atsushi Nishizawa, Yoshito Niwa, Masatake Ohashi, Naoko Ohishi, Masashi Ohkawa, Akira Okutomi, Kouji Onozato, Kenichi Oohara, Norichika Sago, Motoyuki Saijo, Masaaki Sakagami, Shin-ichiro Sakai, Shihori Sakata, Misao Sasaki, Takashi Sato, Masaru Shibata, Hisaaki Shinkai, Kentaro Somiya, Hajime Sotani, Naoshi Sugiyama, Yudai Suwa, Hideyuki Tagoshi, Kakeru Takahashi, Keitaro Takahashi, Tadayuki Takahashi, Hirotaka Takahashi, Ryuichi Takahashi, Ryutaro Takahashi, Akiteru Takamori, Tadashi Takano, Keisuke Taniguchi, Atsushi Taruya, Hiroyuki Tashiro, Mitsuru Tokuda, Masao Tokunari, Morio Toyoshima, Shinji Tsujikawa, Yoshiki Tsunesada, Ken-ichi Ueda, Masayoshi Utashima, Hiroshi Yamakawa, Kazuhiro Yamamoto, Toshitaka Yamazaki, Jun'ichi Yokoyama, Chul-Moon Yoo, Shijun Yoshida, Taizoh Yoshino

TAUP2007: TENTH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS 120 ( 032004 ) 1 - 5 2008

DOI

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Syllabus

Introduction to Physics [S Grade]

School of Advanced Science and Engineering

2025 spring semester
Introduction to Physics

School of Advanced Science and Engineering

2025 spring semester
Theory of Relativity [S Grade]

School of Advanced Science and Engineering

2025 spring semester
Theory of Relativity

School of Advanced Science and Engineering

2025 spring semester
Astrophysics and Cosmology

School of Advanced Science and Engineering

2025 spring semester
Graduation Study [S Grade]

School of Advanced Science and Engineering

2025 full year
Graduation Study

School of Advanced Science and Engineering

2025 full year
Physics: Experiment B [S Grade]

School of Advanced Science and Engineering

2025 full year
Physics: Experiment B

School of Advanced Science and Engineering

2025 full year
Physics : Exercises A [S Grade]

School of Advanced Science and Engineering

2025 full year
Physics : Exercises A

School of Advanced Science and Engineering

2025 full year
Quantum Mechanics A [S Grade]

School of Advanced Science and Engineering

2025 fall semester
Quantum Mechanics A

School of Advanced Science and Engineering

2025 fall semester
Introduction to Physics [S Grade]

School of Advanced Science and Engineering

2025 spring semester
Introduction to Physics

School of Advanced Science and Engineering

2025 spring semester
Scientific Research

School of Advanced Science and Engineering

2025 spring semester
Graduation Study [S Grade]

School of Advanced Science and Engineering

2025 full year
Applied Physics: Experiment B

School of Advanced Science and Engineering

2025 full year
Graduation Study

School of Advanced Science and Engineering

2025 full year
Theory of Relativity [S Grade]

School of Advanced Science and Engineering

2025 spring semester
Theory of Relativity

School of Advanced Science and Engineering

2025 spring semester
Astrophysics and Cosmology

School of Advanced Science and Engineering

2025 spring semester
Applied Physics: Experiment B [S Grade]

School of Advanced Science and Engineering

2025 full year
Physics : Exercises [S Grade]

School of Advanced Science and Engineering

2025 full year
Physics : Exercises

School of Advanced Science and Engineering

2025 full year
Quantum Mechanics A [S Grade]

School of Advanced Science and Engineering

2025 fall semester
Quantum Mechanics A

School of Advanced Science and Engineering

2025 fall semester
Graduation Thesis Fall [S Grade]

School of Advanced Science and Engineering

2025 fall semester
Graduation Thesis Fall

School of Advanced Science and Engineering

2025 fall semester
Graduation Thesis Spring [S Grade]

School of Advanced Science and Engineering

2025 spring semester
Relativity

School of Advanced Science and Engineering

2025 spring semester
Graduation Thesis Spring

School of Advanced Science and Engineering

2025 spring semester
Current Topics in Physics [S Grade]

School of Advanced Science and Engineering

2025 fall semester
Current Topics in Physics

School of Advanced Science and Engineering

2025 fall semester
Master's Thesis (Department of Pure and Applied Physics)

Graduate School of Advanced Science and Engineering

2025 full year
Seminar on Gravitational Physics B

Graduate School of Advanced Science and Engineering

2025 fall semester
Seminar on Gravitational Physics A

Graduate School of Advanced Science and Engineering

2025 spring semester
Advanced Cosmology

Graduate School of Advanced Science and Engineering

2025 spring quarter
Research on Theoretical Astrophysics and Cosmology

Graduate School of Advanced Science and Engineering

2025 full year
Master's Thesis (Department of Pure and Applied Physics)

Graduate School of Advanced Science and Engineering

2025 full year
Seminar on Gravitational Physics B

Graduate School of Advanced Science and Engineering

2025 fall semester
Seminar on Gravitational Physics A

Graduate School of Advanced Science and Engineering

2025 spring semester
Advanced Cosmology

Graduate School of Advanced Science and Engineering

2025 spring quarter
Astrophysics and Cosmology

Graduate School of Advanced Science and Engineering

2025 spring semester
Research on Theoretical Astrophysics and Cosmology

Graduate School of Advanced Science and Engineering

2025 full year
Study Abroad in Physics and Applied Physics A

Graduate School of Advanced Science and Engineering

2025 full year
Research on Theoretical Astrophysics and Cosmology

Graduate School of Advanced Science and Engineering

2025 full year
Study Abroad in Physics and Applied Physics D

Graduate School of Advanced Science and Engineering

2025 full year
Study Abroad in Physics and Applied Physics C

Graduate School of Advanced Science and Engineering

2025 full year
Study Abroad in Physics and Applied Physics B

Graduate School of Advanced Science and Engineering

2025 full year
Celestial Physics II

School of Education

2025 spring semester

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Sub-affiliation

Faculty of Education and Integrated Arts and Sciences School of Education
Faculty of Science and Engineering Graduate School of Advanced Science and Engineering

Research Institute

2024

-

2026

Waseda Research Institute for Science and Engineering Concurrent Researcher

Internal Special Research Projects

重力波による一般相対論とその拡張理論の検証

2024 Antonio De Felice

　View Summary

　宇宙に存在する暗黒物質の性質を重力波によって検証するために，アキシオンという擬スカラー場が光子と結合している場合に，ブラックホールの物理に与える影響を調べた．特に，ブラックホールの準固有振動という物理量を定量的に計算し，アキシオン暗黒物質の性質をブラックホール連星系合体後の重力波の観測から探ることを可能とした．さらに，スカラー場がガウス・ボンネ項と呼ばれる曲率項と結合している系で，ブラックホールの摂動に対する安定性を詳細に調べた．それによって，ブラックホールが安定に存在できるパラメータ領域が明らかにされ，強重力場中での重力理論の検証のための重要な示唆を与えた．これらの研究に加えて，ベクトル場が重力と非自明な結合を持つアインシュタイン・エーテル理論，および一般化されたプロカ理論におけるブラックホールの安定性の解析を行った．特に，ベクトル毛を持つ解のいくつかが棄却されることを新たに示し，重力波の観測からブラックホール解の選別を行う上で重要な寄与を与えた．　上記の研究に加えて，原始ブラックホールの種を生成するような単一場のインフレーション模型において，スカラー場の摂動による1ループ補正が，宇宙背景輻射のような大スケールの曲率揺らぎに与える影響を調べた．特に，経路積分を用いた系統的な解析を行い，1ループ補正が大スケールの揺らぎのスペクトルに与える影響は小さく抑制されることを示した．本研究によって，小スケールの線形揺らぎが単一場インフレーション中に成長しても，それが宇宙背景輻射の温度揺らぎに影響しないことが明らかにされ，原始ブラックホールの研究の上で，重要な成果をもたらした．　上記の研究成果は，8編の学術論文として執筆するだけでなく，2つの国外の研究会においても口頭発表として報告し，特定課題による研究成果の幅広い周知を行なった．
新しい重力理論の構築とその観測的な検証

2023

　View Summary

　一般相対論およびその拡張した理論の検証を行うために，まずはスカラー・テンソル理論に基づくブラックホールと中性子星の解を構築した．その上で，ブラックホール-中性子星連星の合体前に放出される重力波の波形を理論的に計算し，将来の観測によって，中性子星が持ち得るスカラー荷に対してどの程度の制限がつけられるかについて考察した．特に，中性子星が自発的なスカラー化を起こす模型では，重力波の観測から模型のパラメータに強い制限を与えることが可能であることを示した．さらに，ガウス・ボンネ項と呼ばれる2次の曲率項がスカラー場やベクトル場と結合している理論において，静的球対称時空における新しいブラックホール解を発見し，強重力場中での重力理論の検証に重要な示唆を与えた．それに加えて，ワイル曲率項や3次以上の曲率項が存在する系でのブラックホール解について調べ，解が線型摂動に対して不安定になるパラメータ領域について明らかにした．　これらの研究に加えて，曲率の2次の項によって宇宙初期のインフレーションが引き起こされる模型において，ワイル曲率項が果たす役割について調べた．その結果，ワイル項の存在によって線形密度揺らぎが指数関数的に増大し，宇宙背景輻射の観測と整合的な密度揺らぎが生成されないことを示した．この成果は，スカラー曲率の2次の項によって引き起こされるスタロビンスキー・インフレーション模型のユニーク性を示した意味で重要な価値を持つ．　さらに，宇宙後期の進化において，暗黒エネルギーと暗黒物質が結合した模型を新たに構築し，宇宙背景輻射などの観測から両者の結合に関する有意な証拠を得た．　上記の成果は，7編の学術論文として執筆するだけでなく，名古屋大学，タイChulalongkorn大学，京都大学での研究会において口頭発表し，特定課題による研究成果の幅広い周知を行なった．
宇宙初期におけるインフレーションと粒子生成

2000

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　本研究においては、宇宙初期のインフレーションとその直後の前加熱期における粒子生成および時空の揺らぎの発展を様々なモデルにおいて詳しく解析した。特に、カオス的インフレーションモデルおよび高次の曲率が効くインフレーションモデルにおいて、スカラー場が時空のスカラー曲率と非最小結合している系でも効率的な粒子生成が前加熱期中に起こることを示した。また、振動インフレーションおよびナチュラルインフレーションという素粒子理論が起源のモデルにおいて、インフレーション中においてもインフラトン場（インフレーションを担う場）の揺らぎが成長することを見い出した。また、スカラー曲率がインフラトン場以外のスカラー場と結合している、２つのスカラー場が存在する系で、大スケールで時空の揺らぎがインフレーション中に成長しうることを我々は新たに見い出し、これにより結合定数の強さに制限を与えた。また１つの場しか存在しない系では大スケールでの粒子生成および時空の揺らぎの成長が抑えられることを明らかにした。さらに高次元宇宙モデルにおいて、内部空間が球上にコンパクト化されているモデルでのカルツアクライン粒子の生成について調べ、その後の宇宙進化を妨げるような危険な粒子の過度の生成は起こらないことを示した。それに加えて、同様なモデルでのインフレーションと前加熱期での内部空間の振る舞いを調べ、内部空間を安定化させ、かつ宇宙背景輻射のスケール不変な揺らぎを生み出すことができることを示した。また、２つのスカラー場とフェルミオン場が存在するという現実的な系において、フェルミ粒子の生成の詳細な考察を行った。さらに、前加熱期の原始ブラックホールの生成について考察し、結合定数によっては原始ブラックホールの過剰生成が起こることを見出した。これにより、インフレーションのモデルにも制限を与えることが可能になるため、これらの研究は今後極めて重要になると期待される。