Updated on 2022/05/25

写真a

 
KIMURA, Rampei
 
Affiliation
Affiliated organization, Waseda Institute for Advanced Study
Job title
Associate Professor(non-tenure-track)

Concurrent Post

  • Faculty of Science and Engineering   School of Fundamental Science and Engineering

Education

  • 2011.04
    -
    2012.12

    Hiroshima University   Graduate School of Science   Department of Physical Science  

  • 2009.04
    -
    2011.03

    Hiroshima University   Graduate School of Science   Department of Physical Science  

  • 2003.09
    -
    2008.12

    University of Alabama in Huntsville   Physics department  

Research Experience

  • 2018.04
    -
    Now

    Waseda University   Institue for Advanced Study

  • 2016.04
    -
    2018.03

    Tokyo Institute of Technology   School of Science

  • 2014.04
    -
    2016.03

    New York University   Center for Cosmology and Particle Physics   日本学術振興会海外特別研究員

  • 2013.04
    -
    2014.03

    東京大学大学院   理学系研究科附属ビッグバン宇宙国際研究センター   日本学術振興会特別研究員 PD

  • 2013.01
    -
    2013.03

    Hiroshima University   Graduate School of Science

  • 2012.04
    -
    2012.12

    Hiroshima University   Graduate School of Science

▼display all

Professional Memberships

  •  
     
     

    THE PHYSICAL SOCIETY OF JAPAN

 

Research Areas

  • Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics   Cosmology

Research Interests

  • Gravitational theories

  • Cosmology

Papers

  • The linear growth of structure in Projected Massive Gravity

    Yusuke Manita, Rampei Kimura

       2021.12

     View Summary

    In the present paper, we investigate the linear growth of matter fluctuations
    based on a concrete model of the projected massive gravity, which is free of
    the Boulware-Deser ghost and preserves the global Lorentz symmetry. We found
    that at subhorizon scales, the modification to the linear growth is strongly
    suppressed even without nonlinear screening of an additional force. In
    addition, we obtain observational constraints from distance and redshift space
    distortion measurements and find that there is a parameter region that is
    consistent both observationally and theoretically.

  • Reconstruction of Primordial Power Spectrum of curvature perturbation from the merger rate of Primordial Black Hole Binaries

    Rampei Kimura, Teruaki Suyama, Masahide Yamaguchi, Ying-li Zhang

       2021.02

     View Summary

    The properties of primordial curvature perturbations on small scales are
    still unknown while those on large scales have been well probed by the
    observations of the cosmic microwave background anisotropies and the large
    scale structure. In this paper, we propose the reconstruction method of
    primordial curvature perturbations on small scales through the merger rate of
    binary primordial black holes, which could form from large primordial curvature
    perturbation on small scales.

    DOI

  • On Lorentz-invariant bi-spin-2 theories

    Rampei Kimura, Atsushi Naruko, Daisuke Yamauchi

       2020.12

     View Summary

    We investigate a Lorentz invariant action which is quadratic in two rank-2
    symmetric tensor fields in Minkowski spacetime. We apply a scalar-vector-tensor
    decomposition to two tensor fields by virtue of 3-dimensional
    rotation-invariance of Minkowski spacetime and classify theories with seven
    degrees of freedom based on the Hamiltonian analysis. We find two new theories,
    which cannot be mapped from the linearized Hassan-Rosen bigravity. In these
    theories, the new mass interactions can be allowed thanks to the transverse
    diffeomorphism invariance of action.

    DOI

  • Stability of relativistic stars with scalar hairs

    Ryotaro Kase, Rampei Kimura, Seiga Sato, Shinji Tsujikawa

       2020.07  [Refereed]

     View Summary

    We study the stability of relativistic stars in scalar-tensor theories with a
    nonminimal coupling of the form $F(\phi)R$, where $F$ depends on a scalar field
    $\phi$ and $R$ is the Ricci scalar. On a spherically symmetric and static
    background, we incorporate a perfect fluid minimally coupled to gravity as a
    form of the Schutz-Sorkin action. The odd-parity perturbation for the
    multipoles $l \geq 2$ is ghost-free under the condition $F(\phi)>0$, with the
    speed of gravity equivalent to that of light. For even-parity perturbations
    with $l \geq 2$, there are three propagating degrees of freedom arising from
    the perfect-fluid, scalar-field, and gravity sectors. For $l=0, 1$, the
    dynamical degrees of freedom reduce to two modes. We derive no-ghost conditions
    and the propagation speeds of these perturbations and apply them to concrete
    theories of hairy relativistic stars with $F(\phi)>0$. As long as the perfect
    fluid satisfies a weak energy condition with a positive propagation speed
    squared $c_m^2$, there are neither ghost nor Laplacian instabilities for
    theories of spontaneous scalarization and Brans-Dicke (BD) theories with a BD
    parameter $\omega_{\rm BD}>-3/2$ (including $f(R)$ gravity). In these theories,
    provided $0<c_m^2 \le 1$, we show that all the propagation speeds of
    even-parity perturbations are sub-luminal inside the star, while the speeds of
    gravity outside the star are equivalent to that of light.

  • Neutron star cooling in modified gravity theories

    Akira Dohi, Ryotaro Kase, Rampei Kimura, Kazuhiro Yamamoto, Masa-aki Hashimoto

       2020.03  [Refereed]

     View Summary

    We study thermal evolution of isolated neutron stars in scalar-tensor
    theories for the first time. Whether the rapid cooling due to the direct Urca
    process occurs or not is an interesting question in the viewpoint of the
    temperature observation of isolated neutron stars. The cooling effect is
    typically influenced by the proton fraction and the central density. If a fifth
    force is mediated due to modification of gravity, the relation between the
    central density and mass of neutron stars differs from one in general
    relativity, and the cooling curve is also naively expected to be varied. We
    find that an unscreened fifth force near the surface of neutron stars changes
    mass-central density relation, and the direct Urca process can be triggered
    even for neutron stars with smaller mass. This might enable us to test
    gravitational theories with neutron star cooling.

  • Massive gravity with non-minimal coupling

    A. Emir Gumrukcuoglu, Rampei Kimura, Kazuya Koyama

       2020.03  [Refereed]

     View Summary

    We propose new massive gravity theories with 5 dynamical degrees of freedom.
    We evade uniqueness theorems regarding the form of the kinetic and potential
    terms by adopting the "generalized massive gravity" framework, where a global
    translation invariance is broken. By exploiting the rotation symmetry in the
    field space, we determine two novel classes of theories. The first one is an
    extension of generalized massive gravity with a non-minimal coupling. On the
    other hand, the second theory produces a mass term that is different from de
    Rham, Gabadadze, Tolley construction and trivially has 5 degrees of freedom.
    Both theories allows for stable cosmological solutions without infinite strong
    coupling, which are free of ghost and gradient instabilities.

    DOI

  • Redshift space distortions in the presence of non-minimally coupled dark matter

    Fabio Chibana, Rampei Kimura, Masahide Yamaguchi, Daisuke Yamauchi, Shuichiro Yokoyama

       2019.08

     View Summary

    In this paper, we fully investigate cosmological scenarios in which dark<br />
    matter is non-minimally coupled to an extra scalar degree of freedom. The<br />
    interaction is realized by means of conformal and disformal terms in the<br />
    transformed gravitational metric. Considering linear perturbation theory, we<br />
    show that the growth rate of dark matter differs from the uncoupled case and<br />
    that the well-known Kaiser formula undergoes modification. As a result,<br />
    redshift space distortion measurements cease to be a direct probe of the linear<br />
    growth rate of total matter, since the distortion factor has an extra,<br />
    coupling-dependent term. We study the effect of the coupling in three<br />
    cosmological models, two conformally and one disformally coupled, and forecast<br />
    the constraints on the coupling, and other cosmological parameters, from future<br />
    galaxy surveys.

  • On Lorentz-invariant spin-2 theories

    Atsushi Naruko, Rampei Kimura, Daisuke Yamauchi

    Phys. Rev. D 99, 084018 (2019)    2018.12

     View Summary

    We construct Lorentz-invariant massless/massive spin-2 theories in flat<br />
    spacetime. Starting from the most generic action of a rank-2 symmetric tensor<br />
    field whose Lagrangian contains up to quadratic in first derivatives of a<br />
    field, we investigate the possibility of new theories by using the Hamiltonian<br />
    analysis. By imposing the degeneracy of the kinetic matrix and the existence of<br />
    subsequent constraints, we classify theories based on the number of degrees of<br />
    freedom and constraint structures and obtain a wider class of Fierz-Pauli<br />
    theory as well as massless and partially massless theories, whose scalar and/or<br />
    vector degrees of freedom are absent. We also discuss the relation between our<br />
    theories and known massless and massive spin-2 theories.

    DOI

  • Are redshift-space distortions actually a probe of growth of structure?

    Rampei Kimura, Teruaki Suyama, Masahide Yamaguchi, Daisuke Yamauchi, Shuichiro Yokoyama

       2018.08

     View Summary

    We present an impact of coupling between dark matter and a scalar field,<br />
    which might be responsible for dark energy, on measurements of redshift-space<br />
    distortions. We point out that, in the presence of conformal and/or disformal<br />
    coupling, linearized continuity and Euler equations for total matter fluid<br />
    significantly deviate from the standard ones even in the sub-horizon scales. In<br />
    such a case, a peculiar velocity of total matter field is determined not only<br />
    by a logarithmic time derivative of its density perturbation but also by<br />
    density perturbations for both dark matter and baryon, leading to a large<br />
    modification of the physical interpretation of observed data obtained by<br />
    measurements of redshift-space distortions. We reformulate galaxy two-point<br />
    correlation function in the redshift space based on the modified continuity and<br />
    Euler equations. We conclude from the resultant formula that the true value of<br />
    the linear growth rate of large-scale structure cannot be necessarily<br />
    constrained by single-redshift measurements of the redshift-space distortions,<br />
    unless one observes the actual time-evolution of structure.

    DOI

  • Stable cosmological solutions in degenerate theory of gravity

    Ryotaro Kase, Rampei Kimura, Atsushi Naruko, Daisuke Yoshida

    Physics Letters B 783 (2018) 320-325    2018.08

     View Summary

    We study cosmological applications of extended vector-tensor theories, whose<br />
    Lagrangians contain up to two derivatives with respect to metric and vector<br />
    field. We derive background equations under the assumption of homogeneous and<br />
    isotropic universe and study the nature of cosmological perturbations on top of<br />
    the background. We found an example of healthy cosmological solutions in<br />
    non-trivial degenerate theory of gravity for the first time, where those<br />
    perturbations do not suffer from any instabilities, that is, ghost and gradient<br />
    instabilities.

    DOI

  • Ghost-free scalar-fermion interactions

    Rampei Kimura, Yuki Sakakihara, Masahide Yamaguchi

    Phys. Rev. D 98, 044043 (2018)    2018.08

     View Summary

    We discuss a covariant extension of interactions between scalar fields and<br />
    fermions in a flat space-time. We show, in a covariant theory, how to evade<br />
    fermionic ghosts appearing because of the extra degrees of freedom behind a<br />
    fermionic nature even in the Lagrangian with first derivatives. We will give a<br />
    concrete example of a quadratic theory with up to the first derivative of<br />
    multiple scalar fields and a Weyl fermion. We examine not only the maximally<br />
    degenerate condition, which makes the number of degrees of freedom correct, but<br />
    also a supplementary condition guaranteeing that the time evolution takes place<br />
    properly. We also show that proposed derivative interaction terms between<br />
    scalar fields and a Weyl fermion cannot be removed by field redefinitions.

    DOI

  • Ghost free systems with coexisting bosons and fermions

    Rampei Kimura, Yuki Sakakihara, Masahide Yamaguchi

    PHYSICAL REVIEW D   96 ( 4 )  2017.08

     View Summary

    We study the coexistence system of both bosonic and fermionic degrees of freedom. Even if a Lagrangian does not include higher derivatives, fermionic ghosts exist. For a Lagrangian with up to first derivatives, we find the fermionic ghost free condition in Hamiltonian analysis, which is found to be the same as requiring that the equations of motion of fermions be first order in Lagrangian formulation. When fermionic degrees of freedom are present, the uniqueness of time evolution is not guaranteed a priori because of the Grassmann property. We confirm that the additional condition, which is introduced to close Hamiltonian analysis, also ensures the uniqueness of the time evolution of the system.

    DOI

  • Extended vector-tensor theories

    Rampei Kimura, Atsushi Naruko, Daisuke Yoshida

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 1 )  2017.01

     View Summary

    Recently, several extensions of massive vector theory in curved space-time have been proposed in many literatures. In this paper, we consider the most general vector tensor theories that contain up to two derivatives with respect to metric and vector field. By imposing a degeneracy condition of the Lagrangian in the context of ADM decomposition of space-time to eliminate an unwanted mode, we construct a new class of massive vector theories where five degrees of freedom can propagate, corresponding to three for massive vector modes and two for massless tensor modes. We find that the generalized Proca and the beyond generalized Proca theories up to the quartic Lagrangian, which should be included in this formulation, are degenerate theories even in curved space-time. Finally, introducing new metric and vector field transformations, we investigate the properties of thus obtained theories under such transformations.

    DOI

  • Constraint on ghost-free bigravity from gravitational Cherenkov radiation

    Rampei Kimura, Takahiro Tanaka, Kazuhiro Yamamoto, Yasuho Yamashita

    PHYSICAL REVIEW D   94 ( 6 )  2016.09

     View Summary

    We investigate gravitational Cherenkov radiation in a healthy branch of background solutions in the ghost-free bigravity model. In this model, because of the modification of dispersion relations, each polarization mode can possess subluminal phase velocities, and the gravitational Cherenkov radiation could be potentially emitted from a relativistic particle. In the present paper, we derive conditions for the process of the gravitational Cherenkov radiation to occur and estimate the energy emission rate for each polarization mode. We found that the gravitational Cherenkov radiation emitted even from an ultrahigh energy cosmic ray is sufficiently suppressed for the graviton's effective mass less than 100 eV, and the bigravity model with dark matter coupled to the hidden metric is therefore consistent with observations of high energy cosmic rays.

    DOI

  • Vainshtein solutions without superluminal modes

    Gregory Gabadadze, Rampei Kimura, David Pirtskhalava

    PHYSICAL REVIEW D   91 ( 12 )  2015.06

     View Summary

    The Vainshtein mechanism suppresses the fifth force at astrophysical distances, while enabling it to compete with gravity at cosmological scales. Typically, Vainshtein solutions exhibit superluminal perturbations. However, a restricted class of solutions with special boundary conditions was shown to be devoid of the faster-than-light modes. Here we extend this class by finding solutions in a theory of quasidilaton, amended by derivative terms consistent with its symmetries. Solutions with Minkowski asymptotics are not stable, while the ones that exhibit the Vainshtein mechanism by transitioning to cosmological backgrounds are free of ghosts, tachyons, gradient instability, and superluminality, for all propagating modes present in the theory. These solutions require a special choice of the strength and signs of nonlinear terms, as well as a choice of asymptotic cosmological boundary conditions.

    DOI

  • The fate of non-diagonalizable interactions in quasidilaton theory

    Rampei Kimura

       2015.03

     View Summary

    It has been shown that the spherically symmetric solutions in a subclass of<br />
    quasidilaton theory are stable against all degrees of freedom and does not even<br />
    exhibit superluminal propagation. These solutions can be found by switching off<br />
    scalar-tensor interactions, which can not be removed by a local transformation.<br />
    In this paper, we extend the analysis to quasidilaton theory, including<br />
    non-diagonalizable scalar-tensor interactions. We show that all solutions<br />
    inside the Vainshtein radius are problematic : the scalar mode in massive<br />
    graviton suffers from gradient instabilities, the vector mode are infinitely<br />
    strongly coupled vector perturbations, or the Vainshtein mechanism is absent.

  • Self-acceleration with quasidilaton

    Gregory Gabadadze, Rampei Kimura, David Pirtskhalava

    PHYSICAL REVIEW D   90 ( 2 )  2014.07

     View Summary

    Quasidilaton massive gravity is an extension of massive general relativity to a theory with additional scale invariance and approximate internal Galilean symmetry. The theory has a novel self-accelerated solution with the metric indistinguishable (in the decoupling limit) from the de Sitter space, its curvature set by the graviton mass. The spectra of tensor, vector, and scalar perturbations on this solution contain neither ghosts nor gradient instabilities or superluminal modes, for a range of the parameter space. This represents an example of a self-accelerated solution with viable perturbations, attainable within a low-energy effective field theory.

    DOI

  • Cosmology of the proxy theory to massive gravity

    Lavinia Heisenberg, Rampei Kimura, Kazuhiro Yamamoto

    Physical Review D - Particles, Fields, Gravitation and Cosmology   89 ( 10 )  2014.05  [Refereed]

     View Summary

    In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)]. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity, and it represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely, massive gravity and Horndeski theories. We go beyond the regime which was studied in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)] and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is the flat Minkowski solution
    hence, this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions. © 2014 American Physical Society.

    DOI

  • Cosmology of the proxy theory to massive gravity

    Lavinia Heisenberg, Rampei Kimura, Kazuhiro Yamamoto

    PHYSICAL REVIEW D   89 ( 10 )  2014.05

     View Summary

    In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)]. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity, and it represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely, massive gravity and Horndeski theories. We go beyond the regime which was studied in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)] and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is the flat Minkowski solution; hence, this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.

    DOI

  • Derivative interactions in de Rham-Gabadadze-Tolley massive gravity

    Rampei Kimura, Daisuke Yamauchi

    PHYSICAL REVIEW D   88 ( 8 )  2013.10

     View Summary

    We investigate the possibility of a new massive gravity theory with derivative interactions as an extension of de Rham-Gabadadze-Tolley massive gravity. We find the most general Lagrangian of derivative interactions using a Riemann tensor whose cutoff energy scale is Lambda(3), which is consistent with de Rham-Gabadadze-Tolley massive gravity. Surprisingly, this infinite number of derivative interactions can be resummed with the same method in de Rham-Gabadadze-Tolley massive gravity, and remaining interactions contain only two parameters. We show that the equations of motion for scalar and tensor modes in the decoupling limit contain fourth derivatives with respect to spacetime, which implies the appearance of ghosts at Lambda(3). We claim that consistent derivative interactions in de Rham-Gabadadze-Tolley massive gravity have a mass scale M, which is much smaller than the Planck mass M-Pl.

    DOI

  • Constraints on general second-order scalar-tensor models from gravitational Cherenkov radiation

    Rampei Kimura, Kazuhiro Yamamoto

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 7 )  2012.07

     View Summary

    We demonstrate that the general second-order scalar-tensor theories, which have attracted attention as possible modified gravity models to explain the late time cosmic acceleration, could be strongly constrained from the argument of the gravitational Cherenkov radiation. To this end, we consider the purely kinetic coupled gravity and the extended galileon model on a cosmological background. In these models, the propagation speed of tensor mode could be less than the speed of light, which puts very strong constraints from the gravitational Cherenkov radiation.

    DOI

  • Observational constraints on kinetic gravity braiding from the integrated Sachs-Wolfe effect

    Rampei Kimura, Tsutomu Kobayashi, Kazuhiro Yamamoto

    PHYSICAL REVIEW D   85 ( 12 )  2012.06

     View Summary

    The cross correlation between the integrated Sachs-Wolfe (ISW) effect and the large-scale structure is a powerful tool to constrain dark energy and alternative theories of gravity. In this paper, we obtain observational constraints on kinetic gravity braiding from the ISW-large-scale-structure cross correlation. We find that the late-time ISW effect in the kinetic gravity braiding model anticorrelates with large-scale structures in a wide range of parameters, which clearly demonstrates how one can distinguish modified gravity theories from the lambda cold dark matter model using the ISW effect.

    DOI

  • Vainshtein screening in a cosmological background in the most general second-order scalar-tensor theory

    Rampei Kimura, Tsutomu Kobayashi, Kazuhiro Yamamoto

    PHYSICAL REVIEW D   85 ( 2 )  2012.01

     View Summary

    A generic second-order scalar-tensor theory contains a nonlinear derivative self-interaction of the scalar degree of freedom phi a la Galileon models, which allows for the Vainshtein screening mechanism. We investigate this effect on subhorizon scales in a cosmological background, based on the most general second-order scalar-tensor theory. Our analysis takes into account all the relevant nonlinear terms and the effect of metric perturbations consistently. We derive an explicit form of Newton's constant, which in general is time-dependent and hence is constrained from observations, as suggested earlier. It is argued that in the most general case the inverse-square law cannot be reproduced on the smallest scales. Some applications of our results are also presented.

    DOI

  • HALO MODELS IN MODIFIED GRAVITY THEORIES WITH SELF-ACCELERATED EXPANSION

    Tatsuya Narikawa, Rampei Kimura, Tatsunosuke Yano, Kazuhiro Yamamoto

    INTERNATIONAL JOURNAL OF MODERN PHYSICS D   20 ( 12 ) 2383 - 2397  2011.11

     View Summary

    We investigate the structure of halos in the sDGP (self-accelerating branch of the Dvali-Gavadadze-Porrati braneworld gravity) model and the Galileon modified gravity model on the basis of the static and spherically symmetric solutions of the collisionless Boltzmann equation, which reduce to the singular isothermal sphere model and the King model in the limit of Newtonian gravity. The common feature of these halos is that the density of a halo in the outer region is larger (smaller) in the sDGP (Galileon) model, respectively, in comparison with Newtonian gravity. This comes from the suppression (enhancement) of the effective gravity at large distance in the sDGP (Galileon) model, respectively. However, the difference between these modified gravity models and Newtonian gravity only appears outside the halo due to the Vainshtein mechanism, which makes it difficult to distinguish between them. We also discuss the case in which the halo density profile is fixed independently of the gravity model for comparison between our results and previous work.

    DOI

  • Large scale structures in the kinetic gravity braiding model that can be unbraided

    Rampei Kimura, Kazuhiro Yamamoto

    JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS   ( 4 )  2011.04

     View Summary

    We study cosmological consequences of a kinetic gravity braiding model, which is proposed as an alternative to the dark energy model. The kinetic braiding model we study is characterized by a parameter n, which corresponds to the original galileon cosmological model for n = 1. We find that the background expansion of the universe of the kinetic braiding model is the same as the Dvali-Turner's model, which reduces to that of the standard cold dark matter model with a cosmological constant (Lambda CDM model) for n equal to infinity. We also find that the evolution of the linear cosmological perturbation in the kinetic braiding model reduces to that of the Lambda CDM model for n = 1. Then, we focus our study on the growth history of the linear density perturbation as well as the spherical collapse in the nonlinear regime of the density perturbations, which might be important in order to distinguish between the kinetic braiding model and the Lambda CDM model when n is finite. The theoretical prediction for the large scale structure is confronted with the multipole power spectrum of the luminous red galaxy sample of the Sloan Digital Sky survey. We also discuss future prospects of constraining the kinetic braiding model using a future redshift survey like the WFMOS/SuMIRe PFS survey as well as the cluster redshift distribution in the South Pole Telescope survey.

    DOI

  • Quantum Larmor radiation in a conformally flat universe

    Rampei Kimura, Gen Nakamura, Kazuhiro Yamamoto

    PHYSICAL REVIEW D   83 ( 4 )  2011.02

     View Summary

    We investigate the quantum effect on the Larmor radiation from a moving charge in an expanding universe based on the framework of the scalar quantum electrodynamics. A theoretical formula for the radiation energy is derived at the lowest order of the perturbation theory with respect to the coupling constant of the scalar quantum electrodynamics. We evaluate the radiation energy on the background universe so that the Minkowski spacetime transits to the Milne universe, in which the equation of motion for the mode function of the free complex scalar field can be exactly solved in an analytic way. Then, the result is compared with the WKB approach, in which the equation of motion of the mode function is constructed with the WKB approximation which is valid as long as the Compton wavelength is shorter than the Hubble horizon length. This demonstrates that the quantum effect on the Larmor radiation of the order e(2)(h) over bar is determined by a nonlocal integration in time depending on the background expansion. We also compare our result with a recent work by Higuchi and Walker [Phys. Rev. D 80, 105019 (2009)], which investigated the quantum correction to the Larmor radiation from a charged particle in a nonrelativistic motion in a homogeneous electric field.

    DOI

▼display all

Awards

  • Outstanding Presentation Award Gold Prize

    2012.11   RESCEU symposium on general relativity and gravitation JGRG22   "Constraints on general second-order scalar-tensor models from gravitational Cherenkov radiation"

    Winner: 木村蘭平

Research Projects

  • 重力子の質量の起源と宇宙論

    日本学術振興会  科学研究費助成事業(若手研究B)

    Project Year :

    2017.04
    -
    2019.03
     

    木村蘭平

  • 宇宙の加速膨張と重力理論の理論的研究および観測的検証

    日本学術振興会  特別研究員奨励費

    Project Year :

    2012.04
    -
    2013.03
     

    木村蘭平

Presentations

  • Vainshtein screening in Lorentz-invariant massive gravity

    Rampei Kimura  [Invited]

    8th Korea-Japan workshop on Dark Energy 

    Presentation date: 2021.10

  • Vainshtein mechanism in Generalized dRGT massive gravity

    木村蘭平

    物理学会秋季大会 

    Presentation date: 2021.09

  • New graviton mass with broken translation symmetry

     [Invited]

    “Japan-Netherlands symposium on Gravity & Cosmology" 

    Presentation date: 2020.07

    Event date:
    2020.07
     
     
  • On Lorentz-Invariant Spin-2 Theories

    木村蘭平

    22nd International Conference on General Relativity and Gravitation 

    Presentation date: 2019.07

  • On linearized bi-gravity theories

    木村蘭平

    The third NRF-JSPS workshop in particle physics, cosmology, and gravitation 

    Presentation date: 2019.06

  • On Lorentz-invariant spin-2 theories

    木村蘭平

    物理学会第74回年次大会 

    Presentation date: 2019.03

  • New ascpects of massive gravity

    木村蘭平

    FAPESP&JSPS workshop – Dark energy, Dark Matter and Galaxies 

    Presentation date: 2019.02

  • Beyond Fierz-Pauli theory

    木村蘭平

    COSMO 2018 

    Presentation date: 2018.09

  • Beyond Fierz-Pauli theory

    木村蘭平  [Invited]

    The first NRF-JSPS workshop in particle physics, cosmology, and gravitation 

    Presentation date: 2018.07

  • Are redshift-space distortions actually a probe of growth of structure?

    木村蘭平

    Essential next steps for gravity and cosmology 

    Presentation date: 2018.06

  • 赤方偏移歪みで宇宙の大規模構造の成長率を本当に測ることができるのか?

    木村蘭平

    物理学会第73回年次大会 

    Presentation date: 2018.03

  • What can we probe with redshift space distortions?

    木村蘭平

    Gravity/Cosmology workshop, Yamaguchi University 

    Presentation date: 2018.03

  • Are redshift-space distortions actually a probe of growth of structure?

    木村蘭平

    CosPA 

    Presentation date: 2017.12

  • Are redshift-space distortions actually a probe of growth of structure?

    木村蘭平

    JGRG27 

    Presentation date: 2017.11

  • Degenerate fermionic field theory

    木村蘭平

    物理学会秋季大会 

    Presentation date: 2017.09

  • Extended vector-tensor theories

    木村蘭平

    物理学会第72回年次大会 

    Presentation date: 2017.03

  • Ghost-free boson and fermion systems with higher derivatives

    木村蘭平  [Invited]

    Workshop on gravity and cosmology for young researcher 

    Presentation date: 2017.03

  • Ghost-free systems with coexisting boson and fermion

    木村蘭平

    The origin and evolution of the universe 

    Presentation date: 2017.03

  • Constraint on ghost-free bigravity from gravitational Cherenkov radiation

    木村蘭平

    JGRG26 

    Presentation date: 2016.10

  • Gravitational Cherenkov radiation in ghost-free bigravity

    木村蘭平  [Invited]

    Workshop on Particle Physics, Cosmology, and Gravitation 

    Presentation date: 2016.09

  • The Absence of Superluminal Modes in Quasidilaton theory

    木村蘭平

    Marcel Grossmann Meeting 14 

    Presentation date: 2015.08

  • Derivative interactions for a massive graviton

    木村蘭平

    26回理論懇シンポジウム 

    Presentation date: 2013.12

  • Derivative interactions in nonlinear massive gravity

    木村蘭平

    JGRG23 

    Presentation date: 2013.11

  • Inevitable ghost in the decoupling limit of quasi-dilaton theory

    木村蘭平

    COSMO 2013 

    Presentation date: 2013.09

  • Vainshtein solutions and appearance of ghost in quasi-dilaton theory

    木村蘭平

    The 12th Asia Pacific Physics Conferences 

    Presentation date: 2013.07

  • Vainshtein mechanism in quasi-dilaton massive gravity

    木村蘭平

    Mini-workshop “Massive gravity and its cosmological implications” 

    Presentation date: 2013.04

  • Vainshtein mechanism in modified gravity theories

    木村蘭平

    TJ 2012: JAPAN/THAI workshop in cosmology 

    Presentation date: 2012.12

  • Constraints on general second-order scalar-tensor models from gravitational Cherenkov radiation

    木村蘭平

    JGRG 22 

    Presentation date: 2012.11

  • Vainshtein screening in a cosmological background in the most general second- order scalar-tensor theory

    木村蘭平

    COSMO 2012 

    Presentation date: 2012.09

  • Observational constraints on Galileon gravity

    木村蘭平

    YITP International Molecule-type Workshop “Nonlinear massive gravity theory and its observational test” 

    Presentation date: 2012.08

  • Vainshtein screening in a cosmological background in the most general scalar- tensor theory

    木村蘭平

    The Physical Society of Japan 2012 Spring Meeting 

    Presentation date: 2012.03

  • Vainshtein mechanism in a cosmological background in the most general second-order scalar-tensor theory

    木村蘭平

    2012 Asia Pacific School/Workshop on Cosmology and Gravitation 

    Presentation date: 2012.03

  • Vainshtein effect in a cosmological background in the most general second- order scalar-tensor theory

    木村蘭平  [Invited]

    2012 KASI-YITP Joint-Workshop: Cosmology Now and Tomorrow 

    Presentation date: 2012.02

  • Constraints on Kinetic Gravity Braiding Model from the Integrated Sachs- Wolfe Effect

    木村蘭平

    24回理論懇シンポジウム 

    Presentation date: 2011.11

  • Observational Constraints on Kinetic Gravity Braiding Model from the Integrated Sachs-Wolfe Effect

    木村蘭平

    物理学会秋季大会 

    Presentation date: 2011.09

  • Evolution of cosmological perturbations in kinetic gravity braiding model

    木村蘭平

    YIPQS molecule-type workshop, "Cosmological Perturbation and Cosmic Microwave Background" 

    Presentation date: 2011.03

  • Cosmological constraints on kinetic gravity braiding model

    木村蘭平

    INSAM symposium 

    Presentation date: 2011.03

  • Large Scale Structures in Kinetic Gravity Braiding Model

    木村蘭平

    物理学会第66回年次大会 

    Presentation date: 2011.03

  • 大規模構造からのGalileon重力理論の制限

    木村蘭平

    物理学会秋季大会 

    Presentation date: 2010.09

▼display all

Specific Research

  • disformal変換の四脚場形式とその応用

    2019  

     View Summary

    現代物理学の未解決問題である現在の宇宙の加速膨張は、Einsteinの一般相対性理論の重力の法則を変更することで、説明できることが知られています。重力場と他の場を混ぜる変換を行うことで、様々な重力理論と結びついていることが知られています。この重力場とフェルミ粒子の結合を定式化するためには、四脚場による重力理論の形式を用いる必要があります。そのために、本研究ではまずdisformal変換を四脚場で定式化し、Einstein重力と通常のワイル場がこの変換でどのように記述されるかを考察しました。この結果により、高階微分を含む重力とフェルミオンの相互作用がどのように記述できるのかを明らかにできると考えています。

  • 高次元重力理論の新展開

    2019  

     View Summary

    スカラー・テンソル理論は宇宙の加速膨張を記述する有力な候補として知られていますが、理論に存在する任意関数を仮定し検証するというアプローチがとられています。無限の選び方があるため、新たな視点が必要です。高次元の重力理論では、より物理的自由度が多くなるため、低次元にコンパクト化することで、新たな自由度が現れます。そこで、高次元のスカラーテンソル理論からどのような理論が得られるのかを調べ、4次元における有効理論との対応関係を探りました。高次元重力理論から有効理論の導出を行ったことで、宇宙の加速膨張を記述する重力理論のより広い枠組みからの知見を得ることが可能になると期待されます。

  • 曲がった時空におけるフェルミ粒子の理論の構築と宇宙論への応用に関する研究

    2018   山口昌英, 榊原由貴

     View Summary

    宇宙の加速膨張の引き金である正体不明のダークエネルギーは、一般相対性理論だけでは説明できないため、より広い枠組みの重力理論の構築・検証を行うことが、最も重要な課題となっています。これまで一般相対性理論を超える重力理論の研究は多岐に渡り行ってこられましたが、全てボース粒子で記述される理論となっています。素粒子理論の観点からは超対称性理論と呼ばれる、ボース粒子とフェルミ粒子の入れ替えに関する対称性の理論が有力候補として知られているため、フェルミ粒子を含むような重力理論を構築することは非常に重要です。そこで、平坦な時空上でスカラー場とワイル場が相互作用するような理論の一般化を行った結果、これまで知られていた標準理論以外にも、十分な数の拘束条件があれば、不安定性の現れないような理論が存在することを証明し、曲がった時空への応用が可能であることも言及しました。

 

Syllabus

Teaching Experience

  • General Physics A : Mechanics

    早稲田大学 理工学部  

  • Science and Engineering Laboratory

    早稲田大学 理工学部  

  • 宇宙物理概論

    立教大学 理学部  

  • 数理演習1

    法政大学 デザイン工学部 システムデザイン学科  

  • 数学2

    法政大学 デザイン工学部 システムデザイン学科