2024/02/27 更新

写真a

フジタ トモヒロ
藤田 智弘
所属
附属機関・学校 高等研究所
職名
講師(任期付)
メールアドレス
メールアドレス

受賞

  • 若手奨励賞(宇宙線・宇宙物理領域)

    2022年03月   日本物理学会   ゲージ場の宇宙論  

 

論文

  • First test of the consistency relation for the large-scale structure using the anisotropic three-point correlation function of BOSS DR12 galaxies

    Naonori S Sugiyama, Daisuke Yamauchi, Tsutomu Kobayashi, Tomohiro Fujita, Shun Arai, Shin’ichi Hirano, Shun Saito, Florian Beutler, Hee-Jong Seo

    Monthly Notices of the Royal Astronomical Society   524 ( 2 ) 1651 - 1667  2023年06月

     概要を見る

    ABSTRACT

    We present, for the first time, an observational test of the consistency relation for the large-scale structure (LSS) of the Universe through a joint analysis of the anisotropic two- and three-point correlation functions (2PCF and 3PCF) of galaxies. We parameterize the breakdown of the LSS consistency relation in the squeezed limit by Es, which represents the ratio of the coefficients of the shift terms in the second-order density and velocity fluctuations. Es ≠ 1 is a sufficient condition under which the LSS consistency relation is violated. A novel aspect of this work is that we constrain Es by obtaining information about the non-linear velocity field from the quadrupole component of the 3PCF without taking the squeezed limit. Using the galaxy catalogues in the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12, we obtain $E_{\rm s} = -0.92_{-3.26}^{+3.13}$, indicating that there is no violation of the LSS consistency relation in our analysis within the statistical errors. Our parameterization is general enough that our constraint can be applied to a wide range of theories, such as multicomponent fluids, modified gravity theories, and their associated galaxy bias effects. Our analysis opens a new observational window to test the fundamental physics using the anisotropic higher-order correlation functions of galaxy clustering.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • New constraints on cosmological modified gravity theories from anisotropic three-point correlation functions of BOSS DR12 galaxies

    Naonori S Sugiyama, Daisuke Yamauchi, Tsutomu Kobayashi, Tomohiro Fujita, Shun Arai, Shin’ichi Hirano, Shun Saito, Florian Beutler, Hee-Jong Seo

    Monthly Notices of the Royal Astronomical Society   523 ( 2 ) 3133 - 3191  2023年05月

     概要を見る

    ABSTRACT

    We report a new test of modified gravity theories using the large-scale structure of the Universe. This paper is the first attempt to (1) apply a joint analysis of the anisotropic components of galaxy two- and three-point correlation functions (2 and 3PCFs) to actual galaxy data and (2) constrain the non-linear effects of degenerate higher-order scalar-tensor (DHOST) theories on cosmological scales. Applying this analysis to the Baryon Oscillation Spectroscopic Survey (BOSS) data release 12, we obtain the lower bounds of −1.655 < ξt and −0.504 < ξs at the $95{ { \ \rm per\ cent } }$ confidence level on the parameters characterizing the time evolution of the tidal and shift terms of the second-order velocity field. These constraints are consistent with GR predictions of ξt = 15/1144 and ξs = 0. Moreover, they represent a 35-fold and 20-fold improvement, respectively, over the joint analysis with only the isotropic 3PCF. We ensure the validity of our results by investigating various quantities, including theoretical models of the 3PCF, window function corrections, cumulative S/N, Fisher matrices, and statistical scattering effects of mock simulation data. We also find statistically significant discrepancies between the BOSS data and the Patchy mocks for the 3PCF measurement. Finally, we package all of our 3PCF analysis codes under the name hitomi and make them publicly available so that readers can reproduce all the results of this paper and easily apply them to ongoing future galaxy surveys.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • How does SU(N)-natural inflation isotropize the Universe?

    Tomoaki Murata, Tomohiro Fujita, Tsutomu Kobayashi

    Physical Review D   107 ( 4 )  2023年02月

    DOI

  • Perturbation theory of large scale structure in the ΛCDM Universe: Exact time evolution and the two-loop power spectrum

    Matteo Fasiello, Tomohiro Fujita, Zvonimir Vlah

    Physical Review D   106 ( 12 )  2022年12月

    DOI

  • Stochastic formalism for U(1) gauge fields in axion inflation

    Tomohiro Fujita, Kyohei Mukaida, Yuichiro Tada

    Journal of Cosmology and Astroparticle Physics   2022 ( 12 ) 026 - 026  2022年12月

     概要を見る

    Abstract

    We develop the stochastic formalism for U(1) gauge fields that has the Chern-Simons coupling to a rolling pseudo-scalar field during inflation.The Langevin equations for the physical electromagnetic fields are derived and the analytic solutions are studied. Using numerical simulation we demonstrate that the electromagnetic fields averaged over the Hubble scale continuously change their direction and their amplitudes fluctuate around the analytically obtained expectation values.Though the isotropy is spontaneously broken by picking up a particular local Hubble patch, each Hubble patch is understood independent and the isotropy is conserved globally byaveraging all the Hubble patches.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Can primordial parity violation explain the observed cosmic birefringence?

    Tomohiro Fujita, Yuto Minami, Maresuke Shiraishi, Shuichiro Yokoyama

    Physical Review D   106 ( 10 )  2022年11月

     概要を見る

    Recently, the cross-correlation between E- and B-mode polarization of the cosmic microwave background, which is well explained by cosmic birefringence with rotation angle β≈0.3 deg, has been found in cosmic microwave background polarization data. We carefully investigate the possibility of explaining the observed EB correlation by the primordial chiral gravitational waves, which can be generated in the parity-violating theories in the primordial Universe. We found that the chiral gravitational wave scenario does not work due to the overproduction of the BB autocorrelation, which far exceeds the observed one by SPTPol and POLARBEAR.

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Effective treatment of U(1) gauge field and charged particles in axion inflation

    Tomohiro Fujita, Jun'ya Kume, Kyohei Mukaida, Yuichiro Tada

    Journal of Cosmology and Astroparticle Physics   2022 ( 09 ) 023 - 023  2022年09月

     概要を見る

    Abstract

    The axionic inflaton with the Chern-Simons coupling may generate U(1) gauge fields and charged particles simultaneously. In order to incorporate the backreaction from the charged particles on the gauge fields, we develop a procedure to obtain an equilibrium solution for the gauge fields by treating the induced current as effective electric and magnetic conductivities. Introducing mean field approximation, and numerically solving self-consistency equations, we find that the gauge field amplitudes are drastically suppressed. Interestingly, as the production becomes more efficient, the charged particles gain a larger part of the transferred energy from the inflaton and eventually dominate it. Our formalism offers a basis to connect this class of inflationary models to a rich phenomenology such as baryogenesis and magnetogenesis.

    DOI

    Scopus

    12
    被引用数
    (Scopus)
  • Inflation with two-form field: the production of primordial black holes and gravitational waves

    Tomohiro Fujita, Hiromasa Nakatsuka, Ippei Obata, Sam Young

    Journal of Cosmology and Astroparticle Physics   2022 ( 09 ) 017 - 017  2022年09月

     概要を見る

    Abstract

    Antisymmetric tensor field (two-form field) is a ubiquitous component in string theory and generally couples to the scalar sector through its kinetic term. In this paper, we propose a cosmological scenario that the particle production of two-form field, which is triggered by the background motion of the coupled inflaton field, occurs at the intermediate stage of inflation and generates the sizable amount of primordial black holes as dark matter after inflation. We also compute the secondary gravitational waves sourced by the curvature perturbation and show that the resultant power spectra are testable with the future space-based laser interferometers.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Gravitational waves detectable in laser interferometers from axion-SU(2) inflation

    Tomohiro Fujita, Kaname Imagawa, Kai Murai

    Journal of Cosmology and Astroparticle Physics   2022 ( 07 ) 046 - 046  2022年07月

     概要を見る

    Abstract

    Chromo-natural inflation (CNI) is an inflationary model where an axion coupled with SU(2) gauge fields acts as the inflaton. In CNI, the gauge fields have nonzero vacuum expectation values (VEVs), which results in the enhancement of gravitational waves (GWs). The original CNI is ruled out by the Planck observations due to the overproduction of GWs. In this work, we consider an inflationary model where the gauge fields acquire nonzero VEVs after the CMB modes exit the horizon. Moreover, we add to the model another field that dominates the universe and drives inflation after the axion starts to oscillate and the gauge field VEVs vanish. By performing numerical simulations, we find a parameter space where the enhanced GWs do not violate the CMB constraints and can be detected by the future GWs observations such as BBO and ET.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • SU(N) natural inflation

    Tomohiro Fujita, Kyohei Mukaida, Kai Murai, Hiromasa Nakatsuka

    Physical Review D   105 ( 10 )  2022年05月

    DOI

  • Universality of linear perturbations in SU(N) natural inflation

    Tomohiro Fujita, Kai Murai, Ryo Namba

    Physical Review D   105 ( 10 )  2022年05月

    DOI

  • Stochastic effects on observation of ultralight bosonic dark matter

    Hiromasa Nakatsuka, Soichiro Morisaki, Tomohiro Fujita, Jun'ya Kume, Yuta Michimura, Koji Nagano, Ippei Obata

       2022年05月

     概要を見る

    Ultralight bosonic particles are fascinating candidates of dark matter (DM).
    It behaves as classical waves in our Galaxy due to its large number density.
    There have been various methods proposed to search for the wave-like DM, such
    as methods utilizing interferometric gravitational-wave detectors.
    Understanding the characteristics of DM signals is crucial to extract the
    properties of DM from data. While the DM signal is nearly monochromatic with
    the angular frequency of its mass, the amplitude and phase are gradually
    changing due to the velocity dispersion of DMs in our Galaxy halo. The
    stochastic amplitude and phase should be properly taken into account to
    accurately constrain the coupling constant of DM from data. Previous works
    formulated a method to obtain the upper bound on the coupling constant
    incorporating the stochastic effects. One of these works compared the upper
    bound with and without the stochastic effect in a measurement time that is much
    shorter than the variation time scale of the amplitude and phase. In this
    paper, we extend their formulation to arbitrary measurement time and evaluate
    the stochastic effects. Moreover, we investigate the velocity-dependent signal
    for dark photon DM including an uncertainly of the velocity. We demonstrate
    that our method accurately estimates the upper bound on the coupling constant
    with numerical simulations. We also estimate the expected upper bound of the
    coupling constant of axion DM and dark photon DM from future experiments in a
    semi-analytic way. The stochasticity especially affects constraints on a small
    mass region. Our formulation offers a generic treatment of the ultralight
    bosonic DM signal with the stochastic effect.

  • When does the Schwinger preheating occur?

    So Okano, Tomohiro Fujita

    Journal of Cosmology and Astroparticle Physics   2022 ( 03 ) 040 - 040  2022年03月

     概要を見る

    Abstract

    When the inflaton couples to photons and amplifies electric fields, charged particles produced via the Schwinger effect can dominate the universe after inflation, which is dubbed as the Schwinger preheating. Using the hydrodynamic approach for the Boltzmann equation, we numerically study two cases, the Starobinsky inflation model with the kinetic coupling and the Watanabe-Kanno-Soda inflation model. The Schwinger preheating is not observed in the latter model but occurs for a sufficiently large inflaton-photon coupling in the first model. We analytically address its condition and derive a general attractor solution of the electric fields. The occurrence of the Schwinger preheating in the first model is determined by whether the electric fields enter the attractor solution during inflation or not.

    DOI

    Scopus

  • Gravitational wave trispectrum in the axion-SU(2) model

    Tomohiro Fujita, Kai Murai, Ippei Obata, Maresuke Shiraishi

    Journal of Cosmology and Astroparticle Physics   2022 ( 01 ) 007 - 007  2022年01月

     概要を見る

    <jats:title>Abstract</jats:title>
    <jats:p>We study the trispectrum of the gravitational waves (GWs) generated through the dynamics of an axionic spectator field and SU(2) gauge fields during inflation.
    In non-Abelian gauge theory, the gauge fields have four-point self-interactions, which induce the tree-level GW trispectrum.
    We formulate this type of the GW trispectrum including the non-dynamical contributions and evaluate it in the equilateral limit as a unique signal of this model.
    We find that the ratio of the GW trispectrum to the cube of the scalar power spectrum can be as large as 𝒪(10<jats:sup>6</jats:sup>) in the viable parameter space, which could be captured in the CMB observations.</jats:p>

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • First observation and analysis of DANCE: Dark matter Axion search with riNg Cavity Experiment

    Yuka Oshima, Hiroki Fujimoto, Masaki Ando, Tomohiro Fujita, Jun’ya Kume, Yuta Michimura, Soichiro Morisaki, Koji Nagano, Hiromasa Nakatsuka, Atsushi Nishizawa, Ippei Obata, Taihei Watanabe

    Journal of Physics: Conference Series   2156 ( 1 ) 012042 - 012042  2021年12月

     概要を見る

    Abstract

    Dark matter Axion search with riNg Cavity Experiment (DANCE) was proposed to search for axion dark matter [Phys. Rev. Lett. 121, 161301 (2018)]. We aim to detect the rotation and oscillation of optical linear polarization caused by axion-photon coupling with a bow-tie cavity. DANCE can improve the sensitivity to axion-photon coupling constant g for axion mass ma &lt; 10−10 eV by several orders of magnitude compared to the best upper limits at present. A prototype experiment DANCE Act-1 is ongoing to demonstrate the feasibility of the method and to investigate technical noises. The optics was assembled and the performance of the cavity was evaluated. The first 12-day observation was successfully performed in May 2021. We reached $3\times {10}^{-6}{\rm{rad } }/\sqrt{ { \rm{Hz } } }$ at 10 Hz in the one-sided amplitude spectral density of the rotation angle of linear polarization.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Ultralight dark matter searches with KAGRA gravitational wave telescope

    Yuta Michimura, Tomohiro Fujita, Jun’ya Kume, Soichiro Morisaki, Koji Nagano, Hiromasa Nakatsuka, Atsushi Nishizawa, Ippei Obata

    Journal of Physics: Conference Series   2156 ( 1 ) 012071 - 012071  2021年12月

     概要を見る

    Abstract

    Among various dark matter candidates, bosonic ultralight fields with masses below 1eV are well motivated. Recently, a number of novel approaches have been put forward to search for ultralight dark matter candidates using laser interferometers at various scales. Those include our proposals to search for axion-like particles (ALPs) and vector fields with laser interferometric gravitational wave detectors. ALPs can be searched for by measuring the oscillating polarization rotation of laser light. Massive vector fields weakly coupled to the standard model sector can also be searched for by measuring the oscillating forces acting on the suspended mirrors of the interferometers. In this paper, the current status of the activities to search for such ultralight dark matter candidates using a gravitational wave detector in Japan, KAGRA, is reviewed. The analysis of data from KAGRA’s observing run in 2020 to search for vector dark matter, and the installation of polarization optics to the arm cavity transmission ports of the interferometer to search for ALPs in future observing runs are underway.

    DOI

    Scopus

  • Dark matter Axion search with riNg Cavity Experiment DANCE: Design and development of auxiliary cavity for simultaneous resonance of linear polarizations

    Hiroki Fujimoto, Yuka Oshima, Masaki Ando, Tomohiro Fujita, Yuta Michimura, Koji Nagano, Ippei Obata

    Journal of Physics: Conference Series   2156 ( 1 ) 012182 - 012182  2021年10月

     概要を見る

    Axion-like particles (ALPs) are undiscovered pseudo-scalar particles that are
    candidates for ultralight dark matter. ALPs interact with photons slightly and
    cause the rotational oscillation of linearly polarized light. Dark matter Axion
    search with riNg Cavity Experiment (DANCE) searches for ALP dark matter by
    amplifying the rotational oscillation with a bow-tie ring cavity. Simultaneous
    resonance of linear polarizations is necessary to amplify both the carrier
    field and the ALP signal, and to achieve the design sensitivity. The
    sensitivity of the current prototype experiment DANCE Act-1 is less than
    expectation by around three orders of magnitude due to the resonant frequency
    difference between s- and p-polarization in the bow-tie ring cavity. In order
    to tune the resonant frequency difference, the method of introducing an
    auxiliary cavity was proposed. We designed an auxiliary cavity that can cancel
    out the resonant frequency difference and realize simultaneous resonance,
    considering optical loss. We also confirmed that the sensitivity of DANCE Act-1
    with the auxiliary cavity can reach the original sensitivity.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Axion dark matter search using arm cavity transmitted beams of gravitational wave detectors

    Koji Nagano, Hiromasa Nakatsuka, Soichiro Morisaki, Tomohiro Fujita, Yuta Michimura, Ippei Obata

    Physical Review D   104 ( 6 )  2021年09月

     概要を見る

    Axion is a promising candidate for ultralight dark matter which may cause a
    polarization rotation of laser light. Recently, a new idea of probing the axion
    dark matter by optical linear cavities used in the arms of gravitational wave
    detectors has been proposed [Phys. Rev. Lett. 123, 111301 (2019)]. In this
    article, a realistic scheme of the axion dark matter search with the arm cavity
    transmission ports is revisited. Since photons detected by the transmission
    ports travel in the cavity for odd-number of times, the effect of axion dark
    matter on their phases is not cancelled out and the sensitivity at low-mass
    range is significantly improved compared to the search using reflection ports.
    We also take into account the stochastic nature of the axion field and the
    availability of the two detection ports in the gravitational wave detectors.
    The sensitivity to the axion-photon coupling, $g_{a\gamma}$, of the
    ground-based gravitational wave detector, such as Advanced LIGO, with 1-year
    observation is estimated to be $g_{a\gamma} \sim 3\times10^{-12}$ GeV$^{-1}$
    below the axion mass of $10^{-15}$ eV, which improves upon the limit achieved
    by the CERN Axion Solar Telescope.

    DOI

  • Dark matter Axion search with riNg Cavity Experiment DANCE: Development of control system for long-term measurement

    Hiroki Fujimoto, Yuka Oshima, Masaki Ando, Tomohiro Fujita, Yuta Michimura, Koji Nagano, Ippei Obata

       2021年05月

     概要を見る

    Axion-like particles (ALPs) are pseudo-scalar particles that are candidates
    for ultralight dark matter. ALPs interact with photons slightly and cause the
    rotational oscillation of linear polarization. DANCE searches for ALP dark
    matter by enhancing the rotational oscillation in a bow-tie ring cavity. The
    signal to noise ratio of DANCE can be improved by long-term observation, and we
    are planning a year-long observation for the final DANCE. In this document, I
    will report on the control systems of the ring cavity we developed for the
    future long-term observation.

  • Improved sensitivity of interferometric gravitational-wave detectors to ultralight vector dark matter from the finite light-traveling time

    Soichiro Morisaki, Tomohiro Fujita, Yuta Michimura, Hiromasa Nakatsuka, Ippei Obata

    Physical Review D   103 ( 5 )  2021年03月

    DOI

  • Probing axionlike particles via cosmic microwave background polarization

    Tomohiro Fujita, Yuto Minami, Kai Murai, Hiromasa Nakatsuka

    Physical Review D   103 ( 6 ) 063508 - 063508  2021年03月  [査読有り]

     概要を見る

    Axion-like particles (ALPs) rotate linear polarization of photons through the ALP-photon coupling and convert the cosmic microwave background (CMB) $E$-mode to the $B$-mode. We derive the relation between the ALP dynamics and the rotation angle by assuming that the ALP $\phi$ has a quadratic potential, $V=m^2\phi^2/2$. We compute the current and future sensitivity of the CMB measurements to the ALP-photon coupling $g$, which can reach $g=4\times 10^{-21}\,\mathrm{GeV}^{-1}$ for $10^{-32}\,\mathrm{eV}\lesssim m\lesssim 10^{-28}\,\mathrm{eV}$ and extensively exceed the other searches for any mass with $m\lesssim 10^{-25}\,\mathrm{eV}$. We also find that the fluctuation of the ALP field at the observer, which has been neglected in previous studies, can induce the significant isotropic rotation of the CMB polarization. The measurements of isotropic and anisotropic rotation allow us to put bounds on relevant quantities such as the ALP mass $m$ and the ALP density parameter $\Omega_\phi$. In particular, if LiteBIRD detects anisotropic rotation, we obtain the lower limit on the tensor-to -scalar ratio as $r > 5 \times 10^{-9}$.

    DOI

    Scopus

    22
    被引用数
    (Scopus)
  • Chiral gravitational waves produced in a helical magnetogenesis model

    So Okano, Tomohiro Fujita

    Journal of Cosmology and Astroparticle Physics   2021 ( 03 ) 026 - 026  2021年03月

     概要を見る

    Abstract

    We investigate the gravitational wave production induced by the primordial magnetic fields in a parity-violating magnetogenesis model. It is shown that the gravitational waves detectable by LISA, DECIGO or BBO and the magnetic fields strong enough to explain the blazar observation can be simultaneously produced. The magnetic fields and the gravitational waves have the same chirality and their amplitudes are related, which may also be tested by future observations.

    DOI

    Scopus

    14
    被引用数
    (Scopus)
  • Resonant gravitational waves in dynamical Chern–Simons–axion gravity

    Tomohiro Fujita, Ippei Obata, Takahiro Tanaka, Kei Yamada

    Classical and Quantum Gravity   38 ( 4 ) 045010 - 045010  2021年02月  [査読有り]

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Ultralight vector dark matter search with auxiliary length channels of gravitational wave detectors

    Yuta Michimura, Tomohiro Fujita, Soichiro Morisaki, Hiromasa Nakatsuka, Ippei Obata

    Physical Review D   102 ( 10 )  2020年11月

    DOI

  • Axion Dark Matter Search with Interferometrie Gravitational Wave Detectors

    Koji Nagano, Ippei Obata, Tomohiro Fujita, Yuta Michimura

    Journal of Physics: Conference Series   1468 ( 1 ) 012027 - 012027  2020年02月

     概要を見る

    Abstract

    Axion dark matter differentiates the phase velocities of the circular-polarized photons. In [Phys. Rev. Lett. 123, 111301 (2019)], we have proposed a scheme to measure the phase difference by using a linear optical cavity. If the scheme is applied to the Fabry-Perot arm of Advanced LIGO-like (Cosmic-Explorer-like) gravitational wave detector, the potential sensitivity to the axion-photon coupling constant, g, reaches g ≃ 8 × 10−13 GeV−1 (4 × 10−14 GeV−1) at the axion mass m ≃ 3 × 10−13 eV (2 × 10−15 eV) and remains at around this sensitivity for 3 orders of magnitude in mass. Furthermore, its sensitivity has a sharp peak reaching g ≃ 10−14 GeV−1 (8 × 10−17 GeV−1) at m = 1.563 × 10−10 eV (1.563 × 10−11 eV). This sensitivity can be achieved without loosing any sensitivity to gravitational waves.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Wide-angle redshift-space distortions at quasi-linear scales: cross-correlation functions from Zel’dovich approximation

    Atsushi Taruya, Shohei Saga, Michel-Andrès Breton, Yann Rasera, Tomohiro Fujita

    Monthly Notices of the Royal Astronomical Society    2020年01月  [査読有り]

    DOI

    Scopus

    19
    被引用数
    (Scopus)
  • DANCE: Dark matter Axion search with riNg Cavity Experiment

    Yuta Michimura, Yuka Oshima, Taihei Watanabe, Takuya Kawasaki, Hiroki Takeda, Masaki Ando, Koji Nagano, Ippei Obata, Tomohiro Fujita

    16TH INTERNATIONAL CONFERENCE ON TOPICS IN ASTROPARTICLE AND UNDERGROUND PHYSICS (TAUP 2019)   1468  2020年  [査読有り]

     概要を見る

    We have proposed a new approach to search for axion dark matter with an optical ring cavity [Phys. Rev. Lett. 121, 161301 (2018)]. The coupling of photons to axions or axion-like particles makes a modulated difference in the phase velocity between left- and right-handed photons. Our method is to measure this phase velocity difference with a ring cavity, by measuring the resonant frequency difference between two circular polarizations. Our estimation shows that the sensitivity to axion-photon coupling constant g(a gamma) for axion mass m less than or similar to 10(-10) eV can be improved by several orders of magnitude compared with the current best limits. In this paper, we present the principles of the Dark matter Axion search with riNg Cavity Experiment (DANCE) and the status of the prototype experiment, DANCE Act-1.

    DOI

    Scopus

    15
    被引用数
    (Scopus)
  • Primordial tensor non-gaussianity from massive gravity

    Fujita, T., Mizuno, S., Mukohyama, S.

    Journal of Cosmology and Astroparticle Physics   2020 ( 1 )  2020年

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Generation of chiral asymmetry via helical magnetic fields

    Schober, J., Fujita, T., Durrer, R.

    Physical Review D   101 ( 10 )  2020年

    DOI

    Scopus

    14
    被引用数
    (Scopus)
  • Scale-invariant helical magnetic fields from inflation

    Fujita, T., Durrer, R.

    Journal of Cosmology and Astroparticle Physics   2019 ( 9 )  2019年

    DOI

    Scopus

    28
    被引用数
    (Scopus)
  • Hunting Axion Dark Matter with Protoplanetary Disk Polarimetry

    Fujita, T., Tazaki, R., Toma, K.

    Physical Review Letters   122 ( 19 )  2019年

    DOI

    Scopus

    39
    被引用数
    (Scopus)
  • Tensor spectra templates for axion-gauge fields dynamics during inflation

    Fujita, T., Sfakianakis, E.I., Shiraishi, M.

    Journal of Cosmology and Astroparticle Physics   2019 ( 5 )  2019年

     概要を見る

    SU(2) gauge fields can generate large gravitational waves during inflation, if they are coupled to an axion which can be either the inflaton or a spectator field. The shape of the produced tensor power spectrum h depends on the form of the axion potential. We derive analytic expressions and provide general templates for h for various types of the spectator axion potential. Furthermore, we explore the detectability of the oscillatory feature, which is present in h in the case of an axion monodromy model, by possible future CMB B-mode polarization observations.

    DOI

    Scopus

    14
    被引用数
    (Scopus)
  • Axion dark matter search with interferometric gravitational wave detectors

    Nagano, K., Fujita, T., Michimura, Y., Obata, I.

    Physical Review Letters   123 ( 11 )  2019年

    DOI

    Scopus

    55
    被引用数
    (Scopus)
  • Mixed non-gaussianity from axion-gauge field dynamics

    Fujita, T., Namba, R., Obata, I.

    Journal of Cosmology and Astroparticle Physics   2019 ( 4 ) 044 - 044  2019年

    DOI

    Scopus

    16
    被引用数
    (Scopus)
  • Hunting for statistical anisotropy in tensor modes with B -mode observations

    Hiramatsu, T., Yokoyama, S., Fujita, T., Obata, I.

    Physical Review D   98 ( 8 )  2018年

    DOI

    Scopus

    7
    被引用数
    (Scopus)
  • Erratum: Critical constraint on inflationary magnetogenesis (Journal of Cosmology and Astroparticle Physics (2014) (013))

    Fujita, T., Yokoyama, S.

    Journal of Cosmology and Astroparticle Physics   2014 ( 5 )  2014年

    DOI

    Scopus

    9
    被引用数
    (Scopus)

▼全件表示

講演・口頭発表等

  • UV divergence in DHOST & Its Renormalization by EFTofLSS

    T. Fujita, S. Hirano

    JGRG31  

    発表年月: 2022年10月

  • 大規模構造バイアストレーサーのブートストラップ

    藤田智弘, M. Fasiello, Z. Vlah

    日本物理学会  

    発表年月: 2022年09月

  • New Axion Dark Matter Search with Proto-Planetary Disks

    Tomohiro Fujita  [招待有り]

    Astrophysical Polarimetry in the Time-Domain Era  

    発表年月: 2022年09月

    開催年月:
    2022年08月
    -
    2022年09月
  • U(1) gauge field & charged particles in axion inflation

    Tomohiro Fujita

    PASCOS2022  

    発表年月: 2022年07月

  • 日本物理学会 第16回 若手奨励賞 受賞記念講演「ゲージ場の宇宙論」

    藤田智弘  [招待有り]

    日本物理学会  

    発表年月: 2022年03月

    開催年月:
    2022年03月
     
     
  • SU(N)-natural inflationにおける原始重力波生成

    藤田智弘

    第1回「素粒子と重力波」研究会  

    発表年月: 2022年02月

    開催年月:
    2022年02月
     
     
  • SU(N) gauge-natural inflation

    Tomohiro Fujita

    Yukawa International Seminar 2022a "Gravity - The Next Generation-"  

    発表年月: 2022年02月

    開催年月:
    2022年02月
     
     
  • Cosmic Birefringence and Axion Dark Energy

    Tomohiro Fujita  [招待有り]

    8th Korea-Japan workshop on Dark Energy  

    発表年月: 2021年10月

    開催年月:
    2021年10月
     
     
  • SU(N) chromo-natural inflation

    藤田智弘, 中塚洋佑, 向田享平, 村井開

    日本物理学会  

    発表年月: 2021年09月

    開催年月:
    2021年09月
     
     

▼全件表示

共同研究・競争的資金等の研究課題

  • 重力波望遠鏡とレーザー干渉計実験による超軽量ダークマター探索

    日本学術振興会  科学研究費助成事業

    研究期間:

    2020年11月
    -
    2025年03月
     

    道村 唯太, 藤田 智弘, LEONARDI MATTEO, 三代木 伸二

     概要を見る

    2021年度は、昨年度から開発を進めていたデータ解析パイプラインを用いて、KAGRAの観測データを用いたゲージボゾン探索を行った。また、KAGRAに偏光光学系を導入することに成功し、次期観測運転時に重力波観測データに加え、アクシオン観測ができるようになった。さらに、光リング共振器を用いたアクシオン探索の試験観測運転を行うとともに、装置の改良を進めた。
    ゲージボゾン探索では、KAGRAの2020年の観測データを用いている。データ解析はほぼ完了し、上限値の導出も完了した。当時の感度では、未探索領域のゲージボゾン探索には至らなかったものの、実データを用いた解析の初実証ができた。また、上限値の算出にはダークマター信号の確率的なふるまいを考慮に入れる必要があるため、その研究を進めた。これまでスカラー場の確率的なふるまいの研究は進められていたが、ベクトル場での同様な研究は初である。一方で、偽信号と思われる信号検出が多数見つかり、雑音源の特定を進めている。環境チャンネルとの相関を取ることなどにより、これまでに250以上のラインノイズ源の同定に成功した。
    また、KAGRAの2020年の観測の際には不可能だった、アクシオン探索をするための偏光光学系を導入した。KAGRAの3 kmに及ぶ両腕の光共振器の透過光学系に偏光子と光検出器を導入し、アクシオンにより引き起こされる偏光回転のデータが取得できるようになった。
    光リング共振器を用いたアクシオン探索実験DANCEにおいては、2021年5月に12日間に及ぶ試験観測運転を実施した。そのうちの10時間の観測データを解析し、光共振器を用いた探索としては初となる上限値の算出に成功した。また、この試験運転時には、s偏光とp偏光が光リング共振器に同時に共振しないという問題が見つかった。そこで補助共振器を導入することにより同時共振が可能となるように改良した。これにより、1桁以上の感度向上に成功した。

  • 物質由来の原始重力波を用いた初期宇宙探査

    日本学術振興会  科学研究費助成事業

    研究期間:

    2018年04月
    -
    2023年03月
     

    藤田 智弘

     概要を見る

    本研究課題では初期宇宙からやってくる原始重力波の新しい生成メカニズムと、作られた重力波の観測的性質を詳しく調べることが主なテーマである。これまでは主にSU(2)ゲージ場から放出される重力波について調べてきたが、本年度はそれを大きく拡張し、一般のSU(N)ゲージ場が存在するインフレーションのモデルの構築と、そのモデルにおける重力波の生成について研究し2本の論文を出すことができた。概要は以下の通りである。
    (i)これまでゲージ場が背景成分(vev)を持つようなインフレーションモデルはSU(2)の場合であるchromo-natural inflation modelしか知られていなかった。私は共同研究者らとそれを拡張し、一般のSU(N)ゲージ場でも同様の安定解が多数存在することを示した。個別の解はSU(N)におけるSU(2)部分群に対応するため、Nが大きいほど解の多様性は大きくなる。また、解ごとにゲージ場の振幅も異なる。有効ポテンシャル等を用いた解析的な議論と、全ての自由度の時間発展を数値的に解く直接的な計算の両方を行い、両者が一致することも示した。
    (ii)上で見つけたSU(N)の背景解のまわりの線形摂動論を解析し、観測的な示唆を調べた。理論の自由度は大きいものの、曲率ゆらぎや重力波というよく知られた観測量と最低次で結合するのは、背景成分を持つSU(2)部分群の摂動だけであることを示した。さらに上述の通り、背景解はSU(2)のものとは一般に異なる性質を持つが、その違いは(未知の)ゲージ結合定数と縮退しており、一次摂動の範囲ではSU(N)はSU(2)と見分けがつかないという普遍性があることを発見した。しかしながら、摂動の高次効果(ループ効果)を取り入れる、あるいは複数ある背景解の間の遷移が起こる場合はこの縮退は解かれるので、SU(N)固有の観測的示唆が得られる可能性もある。

Misc

  • Spin-2 dark matter from an anisotropic universe in bigravity

    Yusuke Manita, Katsuki Aoki, Tomohiro Fujita, Shinji Mukohyama

    Physical Review D   107 ( 10 )  2023年05月

     概要を見る

    Bigravity is one of the natural extensions of general relativity and contains
    an additional massive spin-2 field which can be a good candidate for dark
    matter. To discuss the production of spin-2 dark matter, we study fixed point
    solutions of the background equations for axisymmetric Bianchi type-I Universes
    in two bigravity theories without Boulware-Deser ghost, i.e., Hassan-Rosen
    bigravity and Minimal Theory of Bigravity. We investigate the local and global
    stability of the fixed points and classify them. Based on the general analysis,
    we propose a new scenario where spin-2 dark matter is produced by the
    transition from an anisotropic fixed point solution to isotropic one. The
    produced spin-2 dark matter can account for all or a part of dark matter and
    can be directly detected by laser interferometers in the same way as
    gravitational waves.

    DOI

  • First Results of Axion Dark Matter Search with DANCE

    Yuka Oshima, Hiroki Fujimoto, Masaki Ando, Tomohiro Fujita, Jun'ya Kume, Yuta Michimura, Soichiro Morisaki, Koji Nagano, Atsushi Nishizawa, Ippei Obata

       2023年03月

     概要を見る

    Axions are one of the well-motivated candidates for dark matter, originally
    proposed to solve the strong \textit{CP} problem in particle physics. Dark
    matter Axion search with riNg Cavity Experiment (DANCE) is a new experimental
    project to search for axion dark matter in the mass range of
    $10^{-17}~\mathrm{eV} < m_a < 10^{-11}~\mathrm{eV}$. We aim to detect the
    rotational oscillation of linearly polarized light caused by the axion-photon
    coupling with a bow-tie cavity. The first results of the prototype experiment,
    DANCE Act-1, are reported from a 24-hour observation. We found no evidence for
    axions and set 95% confidence level upper limits on the axion-photon coupling
    $g_{a \gamma} \lesssim 8 \times 10^{-4}~\mathrm{GeV^{-1 } }$ in
    $10^{-14}~\mathrm{eV} < m_a < 10^{-13}~\mathrm{eV}$. Although the bounds did
    not exceed the current best limits, this work is the first demonstration of
    axion dark matter search with an optical cavity.

  • Effective Field Theory of Large Scale Structure in modified gravity and application to Degenerate Higher-Order Scalar-Tensor theories

    Shin'ichi Hirano, Tomohiro Fujita

       2022年10月

     概要を見る

    In modified gravity, the one-loop matter power spectrum exhibits an
    ultraviolet divergence as shown in the framework of the degenerate higher-order
    scalar-tensor theory. To address this problem, we extend the effective field
    theory of large scale structure to modified gravity theories. We find that new
    counterterms appear and renormalize the ultraviolet divergence as a natural
    consequence of non-linearity in the modified Poisson equation. The renormalized
    one-loop matter power spectrum is useful to test modified gravity theories by
    comparing to observations.

  • Blue-tilted Primordial Gravitational Waves from Massive Gravity

    Tomohiro Fujita, Sachiko Kuroyanagi, Shuntaro Mizuno, Shinji Mukohyama

    Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics   789  2018年08月

     概要を見る

    We study a theory of massive tensor gravitons which predicts blue-tilted and
    largely amplified primordial gravitational waves. After inflation, while their
    mass is significant until it diminishes to a small value, gravitons are diluted
    as non-relativistic matter and hence their amplitude can be substantially
    amplified compared to the massless gravitons which decay as radiation. We show
    that such gravitational waves can be detected by interferometer experiments,
    even if their signal is not observed on the CMB scales.

    DOI

  • Footprint of Two-Form Field: Statistical Anisotropy in Primordial Gravitational Waves

    Ippei Obata, Tomohiro Fujita

    Physical Review D   99 ( 2 )  2018年07月

     概要を見る

    We study the observational signatures of two-form field in the inflationary
    cosmology. In our setup a two-form field is kinetically coupled to a spectator
    scalar field and generates sizable gravitational waves and smaller curvature
    perturbation. We find that the sourced gravitational waves have a distinct
    signature: they are always statistically anisotropic and their spherical
    moments are non-zero for hexadecapole and tetrahexacontapole, while the
    quadrupole moment vanishes. Since their amplitude can reach
    $\mathcal{O}(10^{-3})$ in the tensor-to-scalar ratio, we expect this novel
    prediction will be tested in the next generation of the CMB experiments.

    DOI

  • Optical Ring Cavity Search for Axion Dark Matter

    Ippei Obata, Tomohiro Fujita, Yuta Michimura

    Physical Review Letters   121 ( 16 )  2018年05月

     概要を見る

    We propose a novel experiment to search for axion dark matter which
    differentiates the phase velocities of the left and right-handed polarized
    photons. Our optical cavity measures the difference of the resonant frequencies
    between two circular-polarizations of the laser beam. The design of our cavity
    adopts double-pass configuration to realize a null experiment and give a high
    common mode rejection of environmental disturbances. We estimate the potential
    sensitivity to the axion-photon coupling constant $g_{a\gamma}$ for the axion
    mass $m \lesssim 10^{-10}$ eV. In a low mass range $m \lesssim 10^{-15}$ eV, we
    can achieve $g_{a\gamma} \lesssim 3\times 10^{-16} ~\text{GeV}^{-1}$ which is
    beyond the current bound by several orders of magnitude.

    DOI

  • Quantum Entanglement in Multi-field Inflation

    Nadia Bolis, Tomohiro Fujita, Shuntaro Mizuno, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   2018 ( 9 )  2018年05月

     概要を見る

    We study the emergence of quantum entanglement in multi-field inflation. In
    this scenario, the perturbations of one field contribute to the observable
    curvature perturbation, while multi-field dynamics with the other fields affect
    the curvature perturbation through particle production and entanglement. We
    develop a general formalism which defines the quantum entanglement between the
    perturbations of the multiple fields both in the Heisenberg and Schr\"odinger
    pictures, and show that entanglement between different fields can arise
    dynamically in the context of multi-field inflationary scenarios. We also
    present a simple model in which a sudden change in the kinetic matrix of the
    scalar fields generates entanglement and an oscillatory feature appears in the
    power spectrum of the inflaton perturbation.

    DOI

  • Tensor Non-Gaussianity from Axion-Gauge-Fields Dynamics : Parameter Search

    Aniket Agrawal, Tomohiro Fujita, Eiichiro Komatsu

    Journal of Cosmology and Astroparticle Physics   2018 ( 6 )  2018年02月

     概要を見る

    We calculate the bispectrum of scale-invariant tensor modes sourced by
    spectator SU(2) gauge fields during inflation in a model containing a scalar
    inflaton, a pseudoscalar axion and SU(2) gauge fields. A large bispectrum is
    generated in this model at tree-level as the gauge fields contain a tensor
    degree of freedom, and its production is dominated by self-coupling of the
    gauge fields. This is a unique feature of non-Abelian gauge theory. The shape
    of the tensor bispectrum is approximately an equilateral shape for $3\lesssim
    m_Q\lesssim 4$, where $m_Q$ is an effective dimensionless mass of the SU(2)
    field normalised by the Hubble expansion rate during inflation. The amplitude
    of non-Gaussianity of the tensor modes, characterised by the ratio $B_h/P^2_h$,
    is inversely proportional to the energy density fraction of the gauge field.
    This ratio can be much greater than unity, whereas the ratio from the vacuum
    fluctuation of the metric is of order unity. The bispectrum is effective at
    constraining large $m_Q$ regions of the parameter space, whereas the power
    spectrum constrains small $m_Q$ regions.

    DOI

  • Statistically Anisotropic Tensor Modes from Inflation

    Tomohiro Fujita, Ippei Obata, Takahiro Tanaka, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2018 ( 7 ) 023 - 023  2018年01月

     概要を見る

    We consider the inflationary universe with a spectator scalar field coupled
    to a $U(1)$ gauge field and calculate curvature perturbation and gravitational
    waves (GWs). We find that the sourced GWs can be larger than the one from
    vacuum fluctuation and they are statistically anisotropic as well as linearly
    polarized. The GW power spectrum acquires higher multipole moments as
    $\mathcal{P}_h \propto (1-\cos^2\theta+\cos^4\theta-\cos^6\theta)$ irrespective
    of the model parameters.

    DOI

  • Does Anisotropic "Inflation" Produce a Small Statistical Anisotropy?

    Tomohiro Fujita, Ippei Obata

    Journal of Cosmology and Astroparticle Physics   2018 ( 1 ) 049 - 049  2017年11月

     概要を見る

    Anisotropic inflation is an interesting model with an U(1) gauge field and it
    predicts the statistical anisotropy of the curvature perturbation characterized
    by a parameter $g_*$. However, we find that the background gauge field does not
    follow the classical attractor solution due to the stochastic effect. We
    develop the stochastic formalism of a vector field and solve Langevin and
    Fokker-Planck equations. It is shown that this model is excluded by the CMB
    constraint $g_*\le 10^{-2}$ with a high probability about $99.999\%$.

    DOI

  • Finding the chiral gravitational wave background of an axion-SU(2) inflationary model using CMB observations and laser interferometers

    Ben Thorne, Tomohiro Fujita, Masashi Hazumi, Nobuhiko Katayama, Eiichiro Komatsu, Maresuke Shiraishi

    Physical Review D   97 ( 4 )  2017年07月

     概要を見る

    A detection of B-mode polarization of the Cosmic Microwave Background (CMB)
    anisotropies would confirm the presence of a primordial gravitational wave
    background (GWB). In the inflation paradigm this would be an unprecedented
    probe of the energy scale of inflation as it is directly proportional to the
    power spectrum of the GWB. However, similar tensor perturbations can be
    produced by the matter fields present during inflation, breaking this simple
    relationship. It is therefore important to be able to distinguish between
    different generation mechanisms of the GWB. In this paper, we analyse the
    detectability of a new axion-SU(2) gauge field model using its chiral,
    scale-dependent tensor spectrum. We forecast the detectability of the resulting
    CMB TB and EB cross-correlations by the LiteBIRD satellite, considering the
    effects of residual foregrounds, gravitational lensing, and for the first time
    assess the ability of such an experiment to jointly detect primordial TB and EB
    spectra and self-calibrate its polarimeter. We find that LiteBIRD will be able
    to detect the chiral signal for $r_*>0.03$ with $r_*$ denoting the
    tensor-to-scalar ratio at the peak scale, and that the maximum signal-to-noise
    for $r_*<0.07$ is $\sim 2$. We go on to consider an advanced stage of a
    LISA-like mission, and find that such experiments would complement CMB
    observations by providing sensitivity to GWB chirality on scales inaccessible
    to the CMB. We conclude that in order to use the CMB to distinguish this model
    from a conventional vacuum fluctuation model two-point statistics provide some
    power, but to achieve high statistical significance we would require higher
    order statistics which take advantage of the model's non-Gaussianity. On the
    other hand, in the case of a spectrum peaked at very small scales, inaccessible
    to the CMB, a highly significant detection could be made using space-based
    laser interferometers.

    DOI

  • Large Tensor Non-Gaussianity from Axion-Gauge Fields Dynamics

    Aniket Agrawal, Tomohiro Fujita, Eiichiro Komatsu

    Physical Review D   97 ( 10 )  2017年07月

     概要を見る

    We show that an inflation model in which a spectator axion field is coupled
    to an SU(2) gauge field produces a large three-point function (bispectrum) of
    primordial gravitational waves, $B_{h}$, on the scales relevant to the cosmic
    microwave background experiments. The amplitude of the bispectrum at the
    equilateral configuration is characterized by
    $B_{h}/P_h^2=\mathcal{O}(10)\times \Omega_A^{-1}$, where $\Omega_A$ is a
    fraction of the energy density in the gauge field and $P_h$ is the power
    spectrum of gravitational waves produced by the gauge field.

    DOI

  • Does the detection of primordial gravitational waves exclude low energy inflation?

    Tomohiro Fujita, Ryo Namba, Yuichiro Tada

    Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics   778  2017年05月

     概要を見る

    We show that a detectable tensor-to-scalar ratio $(r\ge 10^{-3})$ on the CMB
    scale can be generated even during extremely low energy inflation which
    saturates the BBN bound $\rho_{\rm inf}\approx (30 {\rm MeV})^4$. The source of
    the gravitational waves is not quantum fluctuations of graviton but those of
    $SU(2)$ gauge fields, energetically supported by coupled axion fields. The
    curvature perturbation, the backreaction effect and the validity of
    perturbative treatment are carefully checked. Our result indicates that
    measuring $r$ alone does not immediately fix the inflationary energy scale.

    DOI

  • Very Massive Tracers and Higher Derivative Biases

    Tomohiro Fujita, Valentin Mauerhofer, Leonardo Senatore, Zvonimir Vlah, Raul Angulo

    Journal of Cosmology and Astroparticle Physics   2020 ( 1 )  2016年09月

     概要を見る

    Most of the upcoming cosmological information will come from analyzing the
    clustering of the Large Scale Structures (LSS) of the universe through LSS or
    CMB observations. It is therefore essential to be able to understand their
    behavior with exquisite precision. The Effective Field Theory of Large Scale
    Structures (EFTofLSS) provides a consistent framework to make predictions for
    LSS observables in the mildly non-linear regime. In this paper we focus on
    biased tracers. We argue that in calculations at a given order in the dark
    matter perturbations, highly biased tracers will underperform because of their
    larger higher derivative biases. A natural prediction of the EFTofLSS is
    therefore that by simply adding higher derivative biases, all tracers should
    perform comparably well. We implement this prediction for the halo-halo and the
    halo-matter power spectra at one loop, and the halo-halo-halo,
    halo-halo-matter, and halo-matter-matter bispectra at tree-level, and compare
    with simulations. We find good agreement with the prediction: for all tracers,
    we are able to match the bispectra up to $k\simeq0.17\,h/$Mpc at $z=0$ and the
    power spectra to a higher wavenumber.

    DOI

  • Primordial Gravitational Waves from Axion-Gauge Fields Dynamics

    Emanuela Dimastrogiovanni, Matteo Fasiello, Tomohiro Fujita

    Journal of Cosmology and Astroparticle Physics   2017 ( 1 )  2016年08月

     概要を見る

    Inspired by the chromo-natural inflation model of Adshead&Wyman, we reshape
    its scalar content to relax the tension with current observational bounds.
    Besides an inflaton, the setup includes a spectator sector in which an axion
    and SU(2) gauge fields are coupled via a Chern-Simons-type term. The result is
    a viable theory endowed with an alternative production mechanism for
    gravitational waves during inflation. The gravitational wave signal sourced by
    the spectator fields can be much larger than the contribution from standard
    vacuum fluctuations, it is distinguishable from the latter on the basis of its
    chirality and, depending on the theory parameters values, also its tilt. This
    production process breaks the well-known relation between the tensor-to-scalar
    ratio and the energy scale of inflation. As a result, even if the Hubble rate
    is itself too small for the vacuum to generate a tensor amplitude detectable by
    upcoming experiments, this model still supports observable gravitational waves.

    DOI

  • Hubble induced mass after inflation in spectator field models

    Tomohiro Fujita, Keisuke Harigaya

    Journal of Cosmology and Astroparticle Physics   2016 ( 12 )  2016年07月

     概要を見る

    Spectator field models such as the curvaton scenario and the modulated
    reheating are attractive scenarios for the generation of the cosmic curvature
    perturbation, as the constraints on inflation models are relaxed. In this
    paper, we discuss the effect of Hubble induced masses on the dynamics of
    spectator fields after inflation. We pay particular attention to the Hubble
    induced mass by the kinetic energy of an oscillating inflaton, which is
    generically unsuppressed but often overlooked. In the curvaton scenario, the
    Hubble induced mass relaxes the constraint on the property of the inflaton and
    the curvaton, such as the reheating temperature and the inflation scale. We
    comment on the implication of our discussion for baryogenesis in the curvaton
    scenario. In the modulated reheating, the predictions of models e.g. the
    non-gaussianity can be considerably altered. Furthermore, we propose a new
    model of the modulated reheating utilizing the Hubble induced mass which
    realizes a wide range of the local non-gaussianity parameter.

    DOI

  • Fermionic Schwinger effect and induced current in de Sitter space

    Takahiro Hayashinaka, Tomohiro Fujita, Jun'ichi Yokoyama

    Journal of Cosmology and Astroparticle Physics   2016 ( 7 )  2016年03月

     概要を見る

    We explore Schwinger effect of spin 1/2 charged particles with static
    electric field in 1+3 dimensional de Sitter spacetime. We analytically
    calculate the vacuum expectation value of the spinor current which is induced
    by the produced particles in the electric field. The renormalization is
    performed with the adiabatic subtraction scheme. We find that the current
    becomes negative, namely it flows in the direction opposite to the electric
    field, if the electric field is weaker than a certain threshold value depending
    on the fermion mass, which is also known to happen in the case of scalar
    charged particles in 1+3 de Sitter spacetime. Contrary to the scalar case,
    however, the IR hyperconductivity is absent in the spinor case.

    DOI

  • Pre-reheating Magnetogenesis in the Kinetic Coupling Model

    Tomohiro Fujita, Ryo Namba

    Physical Review D   94 ( 4 )  2016年02月

     概要を見る

    Recent blazar observations provide growing evidence for the presence of
    magnetic fields in the extragalactic regions. While a natural speculation is to
    associate the production to inflationary physics, it has been known that
    magnetogenesis solely from inflation is quite challenging. We therefore study a
    model in which a non-inflaton field $\chi$ coupled to the electromagnetic field
    through its kinetic term, $-I^2(\chi) F^2 /4$, continues to move after
    inflation until the completion of reheating. This leads to a post-inflationary
    amplification of the electromagnetic field. We compute all the relevant
    contributions to the curvature perturbation, including gravitational
    interactions, and impose the constraints from the CMB scalar fluctuations on
    the strength of magnetic fields. We, for the first time, explicitly verify both
    the backreaction and CMB constraints in a simple yet successful magnetogenesis
    scenario without invoking a dedicated low-scale inflationary model in the
    weak-coupling regime of the kinetic coupling model.

    DOI

  • Large-scale magnetic fields can explain the baryon asymmetry of the Universe

    Tomohiro Fujita, Kohei Kamada

    Physical Review D   93 ( 8 )  2016年02月

     概要を見る

    Helical hypermagnetic fields in the primordial Universe can produce the
    observed amount of baryon asymmetry through the chiral anomaly without any
    ingredients beyond the standard model of particle physics. While they generate
    no $B-L$ asymmetry, the generated baryon asymmetry survives the spharelon
    washout effect, because the generating process remains active until the
    electroweak phase transition. Solving the Boltzmann equation numerically and
    finding an attractor solution, we show that the baryon asymmetry of our
    Universe can be explained, if the present large-scale magnetic fields indicated
    by the blazar observations have a negative helicity and existed in the early
    Universe before the electroweak phase transition. We also derive the upper
    bound on the strength of the helical magnetic field, which is tighter than the
    cosmic microwave background constraint, to avoid the overproduction of baryon
    asymmetry.

    DOI

  • Spatially covariant theories of gravity: disformal transformation, cosmological perturbations and the Einstein frame

    Tomohiro Fujita, Xian Gao, Jun'ichi Yokoyama

    Journal of Cosmology and Astroparticle Physics   2016 ( 2 )  2015年11月

     概要を見る

    We investigate the cosmological background evolution and perturbations in a
    general class of spatially covariant theories of gravity, which propagates two
    tensor modes and one scalar mode. We show that the structure of the theory is
    preserved under the disformal transformation. We also evaluate the primordial
    spectra for both the gravitational waves and the curvature perturbation, which
    are invariant under the disformal transformation. Due to the existence of
    higher spatial derivatives, the quadratic Lagrangian for the tensor modes
    itself cannot be transformed to the form in the Einstein frame. Nevertheless,
    there exists a one-parameter family of frames in which the spectrum of the
    gravitational waves takes the standard form in the Einstein frame.

    DOI

  • Consistent generation of magnetic fields in axion inflation models

    Tomohiro Fujita, Ryo Namba, Yuichiro Tada, Naoyuki Takeda, Hiroyuki Tashiro

    Journal of Cosmology and Astroparticle Physics   2015 ( 5 )  2015年03月

     概要を見る

    There has been a growing evidence for the existence of magnetic fields in the
    extra-galactic regions, while the attempt to associate their origin with the
    inflationary epoch alone has been found extremely challenging. We therefore
    take into account the consistent post-inflationary evolution of the magnetic
    fields that are originated from vacuum fluctuations during inflation. In the
    model of our interest, the electromagnetic (EM) field is coupled to a
    pseudo-scalar inflaton $\phi$ through the characteristic term $\phi F\tilde F$,
    breaking the conformal invariance. This interaction dynamically breaks the
    parity and enables a continuous production of only one of the polarization
    states of the EM field through tachyonic instability. The produced magnetic
    fields are thus helical. We find that the dominant contribution to the observed
    magnetic fields in this model comes from the modes that leave the horizon near
    the end of inflation, further enhanced by the tachyonic instability right after
    the end of inflation. The EM field is subsequently amplified by parametric
    resonance during the period of inflaton oscillation. Once the thermal plasma is
    formed (reheating), the produced helical magnetic fields undergo a turbulent
    process called inverse cascade, which shifts their peak correlation scales from
    smaller to larger scales. We consistently take all these effects into account
    within the regime where the perturbation of $\phi$ is negligible and obtain
    $B_{\rm eff} \sim 10^{-19}$G, indicating the necessity of additional mechanisms
    to accommodate the observations.

    DOI

  • Can a spectator scalar field enhance inflationary tensor mode?

    Tomohiro Fujita, Jun'ichi Yokoyama, Shuichiro Yokoyama

    Progress of Theoretical and Experimental Physics   2015 ( 4 )  2014年11月

     概要を見る

    We consider the possibility of enhancing the inflationary tensor mode by
    introducing a spectator scalar field with a small sound speed which induces
    gravitational waves as a second order effect. We analytically obtain the power
    spectra of gravitational waves and curvature perturbation induced by the
    spectator scalar field. We found that the small sound speed amplifies the
    curvature perturbation much more than the tensor mode and the current
    observational constraint forces the induced gravitational waves to be
    negligible compared with those from the vacuum fluctuation during inflation.

    DOI

  • Probing Beyond Standard Model via Hawking Radiated Gravitational Waves

    Tomohiro Fujita

       2014年07月

     概要を見る

    We propose a novel technique to probe the beyond standard model (BSM) of
    particle physics. The mass spectrum of unknown BSM particles can be scanned by
    observing gravitational waves (GWs) emitted by Hawking radiation of black
    holes. This is because information on the radiation of the BSM particles is
    imprinted in the spectrum of the GWs. We fully calculate the GW spectrum from
    evaporating black holes taking into account the greybody factor. As an
    observationally interesting application, we consider primordial black holes
    which evaporate in the very early universe. In that case, since the frequencies
    of GWs are substantially redshifted, the GWs emitted with the BSM energy scales
    become accessible by observations.

  • Non-perturbative approach for curvature perturbations in stochastic-$δN$ formalism

    Tomohiro Fujita, Masahiro Kawasaki, Yuichiro Tada

    Journal of Cosmology and Astroparticle Physics   2014 ( 10 )  2014年05月

     概要を見る

    In our previous paper, we have proposed a new algorithm to calculate the
    power spectrum of the curvature perturbations generated in inflationary
    universe with use of the stochastic approach. Since this algorithm does not
    need the perturbative expansion with respect to the inflaton fields on
    super-horizon scale, it works even in highly stochastic cases. For example,
    when the curvature perturbations are very large or the non-Gaussianities of the
    curvature perturbations are sizable, the perturbative expansion may break down
    but our algorithm enables to calculate the curvature perturbations. We apply it
    to two well-known inflation models, chaotic and hybrid inflation, in this
    paper. Especially for hybrid inflation, while the potential is very flat around
    the critical point and the standard perturbative computation is problematic, we
    successfully calculate the curvature perturbations.

    DOI

  • Curvaton in large field inflation

    Tomohiro Fujita, Masahiro Kawasaki, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2014 ( 9 )  2014年04月

     概要を見る

    We comprehensively explore the quadratic curvaton models in the chaotic
    inflation. In the light of the BICEP2 result $r \approx 0.2$, all model
    parameters and relevant observables are computed. It is found the curvaton
    field value is constrained into a narrow range, $\sigma_* =
    \mathcal{O}(10^{-2}$-$10^{-1})$ and the running of the spectral index is $n_s'
    \gtrsim -10^{-3}$. We show that if the curvaton is added, the models are
    heavily degenerated on the $n_s$ - $r$ plane. However, introducing a new plane,
    the degeneracy can be resolved. To distinguish the curvaton models, precise
    measurements of not only $r$ but also $n_s'$ and the tensor tilt $n_T$ are
    required.

    DOI

  • Is there supercurvature mode of massive vector field in open inflation?

    Daisuke Yamauchi, Tomohiro Fujita, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   2014 ( 3 )  2014年02月

     概要を見る

    We investigate the Euclidean vacuum mode functions of a massive vector field
    in a spatially open chart of de Sitter spacetime. In the one-bubble open
    inflationary scenario that naturally predicts a negative spatial curvature
    after a quantum tunneling, it is known that a light scalar field has the
    so-called supercurvature mode, i.e. an additional discrete mode which describes
    fluctuations over scales larger than the spatial curvature scale. If such
    supercurvature modes exist for a vector field with a sufficiently light mass,
    then they would decay slower and easily survive the inflationary era. However,
    the existence of supercurvature mode strongly depends on details of the system.
    To clarify whether a massive vector field has supercurvature modes, we consider
    a U(1) gauge field with gauge and conformal invariances spontaneously broken
    through the Higgs mechanism, and present explicit expressions for the Euclidean
    vacuum mode functions. We find that, for any values of the vector field mass,
    there is no supercurvature mode. In the massless limit, the absence of
    supercurvature modes in the scalar sector stems from the gauge symmetry.

    DOI

  • Critical constraint on inflationary magnetogenesis

    Tomohiro Fujita, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2014 ( 3 )  2014年02月

     概要を見る

    Recently, there are several reports that the cosmic magnetic fields on Mpc
    scale in void region is larger than $\sim 10^{-15}$G with an uncertainty of a
    few orders from the current blazar observations. On the other hand, in
    inflationary magnetogenesis models, additional primordial curvature
    perturbations are inevitably produced from iso-curvature perturbations due to
    generated electromagnetic fields. We explore such induced curvature
    perturbations in a model independent way and obtained a severe upper bound for
    the energy scale of inflation from the observed cosmic magnetic fields and the
    observed amplitude of the curvature perturbation, as $\rho_{\rm inf}^{1/4} <
    30{\rm GeV} \times (B_{\rm obs}/10^{-15}{\rm G})^{-1}$ where $B_{\rm obs}$ is
    the strength of the magnetic field at present. Therefore, without a dedicated
    low energy inflation model or an additional amplification of magnetic fields
    after inflation, inflationary magnetogenesis on Mpc scale is generally
    incompatible with CMB observations.

    DOI

  • Void magnetic field and its primordial origin in inflation

    Tomohiro Fujita

       2014年01月

     概要を見る

    Since magnetic fields in galaxies, galactic clusters and even void regions
    are observed, theoretical attempts to explain their origin are strongly
    motivated. It is interesting to consider that inflation is responsible for the
    origin of the magnetic fields as well as the density perturbation. However, it
    is known that inflationary magnetogenesis suffers from several problems. We
    explore these problems by using a specific model, namely the kinetic coupling
    model, and show how the model is constrained. Model independent arguments are
    also discussed.

  • Baryon Asymmetry, Dark Matter, and Density Perturbation from PBH

    Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki, Ryo Matsuda

    Physical Review D - Particles, Fields, Gravitation and Cosmology   89 ( 10 )  2014年01月

     概要を見る

    We investigate the consistency of a scenario in which the baryon asymmetry,
    dark matters, as well as the cosmic density perturbation are generated
    simultaneously through the evaporation of primordial black holes (PBHs). This
    scenario can explain the coincidence of the dark matter and the baryon density
    of the universe, and is free from the isocurvature perturbation problem. We
    show that this scenario predicts the masses of PBHs, right-handed neutrinos and
    dark matters, the Hubble scale during inflation, the non-gaussianity and the
    running of the spectral index. We also discuss the testability of the scenario
    by detecting high frequency gravitational waves from PBHs.

    DOI

  • A new algorithm for calculating the curvature perturbations in stochastic inflation

    Tomohiro Fujita, Masahiro Kawasaki, Yuichiro Tada, Tomohiro Takesako

    Journal of Cosmology and Astroparticle Physics   2013 ( 12 )  2013年08月

     概要を見る

    We propose a new approach for calculating the curvature perturbations
    produced during inflation in the stochastic formalism. In our formalism, the
    fluctuations of the e-foldings are directly calculated without perturbatively
    expanding the inflaton field and they are connected to the curvature
    perturbations by the $\delta N$ formalism. The result automatically includes
    the contributions of the higher order perturbations because we solve the
    equation of motion non-perturbatively. In this paper, we analytically prove
    that our result (the power spectrum and the nonlinearity parameter) is
    consistent with the standard result in single field slow-roll inflation. We
    also describe the algorithm for numerical calculations of the curvature
    perturbations in more general inflation models.

    DOI

  • Large Scale Cosmic Perturbation from Evaporation of Primordial Black Holes

    Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki

    Physical Review D - Particles, Fields, Gravitation and Cosmology   88 ( 12 )  2013年06月

     概要を見る

    We present a novel mechanism to generate the cosmic perturbation from
    evaporation of primordial black holes. A mass of a field is fluctuated if it is
    given by a vacuum expectation value of a light scalar field because of the
    quantum fluctuation during inflation. The fluctuated mass causes variations of
    the evaporation time of the primordial black holes. Therefore provided the
    primordial black holes dominate the universe when they evaporate, primordial
    cosmic perturbations are generated. We find that the amplitude of the large
    scale curvature perturbation generated in this scenario can be consistent with
    the observed value. Interestingly, our mechanism works even if all fields which
    are responsible for inflation and the generation of the cosmic perturbation are
    decoupled from the visible sector except for the gravitational interaction. An
    implication to the running spectral index is also discussed.

    DOI

  • Higher order statistics of curvature perturbations in IFF model and its Planck constraints

    Tomohiro Fujita, Shuichiro Yokoyama

    Journal of Cosmology and Astroparticle Physics   2013 ( 9 )  2013年06月

     概要を見る

    We compute the power spectrum P_\zeta, and non-linear parameters f_nl and
    \tau_nl of the curvature perturbation induced during inflation by the
    electromagnetic fields in the kinetic coupling model (IFF model). By using the
    observational result of P_\zeta, f_nl and \tau_nl reported by the Planck
    collaboration, we study the constraint on the model comprehensively.
    Interestingly, if the single slow-rolling inflaton is responsible for the
    observed P_\zeta, the constraint from \tau_nl is most stringent. We also find a
    general relationship between f_nl and \tau_nl generated in this model. Even if
    f_nl \sim O(1), a detectable \tau_nl can be produced.

    DOI

  • Universal upper limit on inflation energy scale from cosmic magnetic field

    Tomohiro Fujita, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   2012 ( 10 )  2012年05月

     概要を見る

    Recently observational lower bounds on the strength of cosmic magnetic fields
    were reported, based on gamma-ray flux from distant blazars. If inflation is
    responsible for the generation of such magnetic fields then the inflation
    energy scale is bounded from above as rho_{inf}^{1/4} < 2.5 times 10^{-7}M_{Pl}
    times (B_{obs}/10^{-15}G)^{-2} in a wide class of inflationary magnetogenesis
    models, where B_{obs} is the observed strength of cosmic magnetic fields. The
    tensor-to-scalar ratio is correspondingly constrained as r< 10^{-19} times
    (B_{obs}/10^{-15}G)^{-8}. Therefore, if the reported strength B_{obs} \geq
    10^{-15}G is confirmed and if any signatures of gravitational waves from
    inflation are detected in the near future, then our result indicates some
    tensions between inflationary magnetogenesis and observations.

    DOI

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  • 理工学術院   先進理工学部

特定課題制度(学内資金)

  • 赤外線あるいは触覚で鑑賞可能な温度分布による美術作品の研究と製作

    2022年  

     概要を見る

    本プロジェクトでは科学と現代美術との境界領域を開拓する新しい試みとして、基礎科学に立脚した視点から作品コンセプトを構築し、実際の美術作品の制作まで行い、その成果を自然科学・人文科学の両面から考察する。地球上の多くの生物は太陽から発される光に適用進化した結果、可視光線を用いた視覚を備えているが、太陽より大きな恒星の周囲に住む生命は赤外線に対する感覚を進化させると想定される。このような観点から赤外線で視える美術として、温度分布による「絵画」を研究製作している。特に本特定課題の予算を用いて、電流を熱流に変換する半導体素子であるペルチェ素子や、鑑賞する際に触る対象となる漆塗りの長板を購入した。