Updated on 2022/10/31

写真a

 
IZUMI Keisuke
 
Organization
Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI) Lecturer
Graduate School
Graduate School of Mathematics
Title
Lecturer

Degree 3

  1. 博士(理学) ( 2009.3   京都大学 ) 

  2. 修士(理学) ( 2006.3   京都大学 ) 

  3. 学士(理学) ( 2004.3   京都大学 ) 

Research Interests 2

  1. 宇宙論

  2. 重力理論

Research History 1

  1. Nagoya University   Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI)   Lecturer

    2021.8

Education 3

  1. Kyoto University

    2006.4 - 2009.3

  2. Kyoto University

    2004.4 - 2006.3

  3. Kyoto University   Faculty of Science

    2000.4 - 2004.3

 

Papers 65

  1. Brane dynamics of holographic BCFTs

    Izumi Keisuke, Shiromizu Tetsuya, Suzuki Kenta, Takayanagi Tadashi, Tanahashi Norihiro

    JOURNAL OF HIGH ENERGY PHYSICS   ( 10 )   2022.10

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    Language:Japanese  

    DOI: 10.1007/JHEP10(2022)050

    Web of Science

  2. Four types of attractive gravity probe surfaces

    Lee Kangjae, Shiromizu Tetsuya, Izumi Keisuke, Yoshino Hirotaka, Tomikawa Yoshimune

    PHYSICAL REVIEW D   Vol. 106 ( 6 )   2022.9

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  3. Asymptotic behavior of null geodesics near future null infinity. II. Curvatures, photon surface, and dynamically transversely trapping surface

    Amo Masaya, Shiromizu Tetsuya, Izumi Keisuke, Yoshino Hirotaka, Tomikawa Yoshimune

    PHYSICAL REVIEW D   Vol. 105 ( 6 )   2022.3

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  4. Invertible field transformations with derivatives: necessary and sufficient conditions Invited Reviewed International coauthorship

    Eugeny Babichev, Keisuke Izumi, Norihiro Tanahashi, Masahide Yamaguchi

    Advances in Theoretical and Mathematical Physics   Vol. Volume 25 (2021) ( Number 2 ) page: 309   2022.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    We formulate explicitly the necessary and sufficient conditions for the local
    invertibility of a field transformation involving derivative terms. Our
    approach is to apply the method of characteristics of differential equations,
    by treating such a transformation as differential equations that give new
    variables in terms of original ones. The obtained results generalise the
    well-known and widely used inverse function theorem. Taking into account that
    field transformations are ubiquitous in modern physics and mathematics, our
    criteria for invertibility will find many useful applications.

    DOI: doi.org/10.4310/ATMP.2021.v25.n2.a2

    arXiv

    Other Link: http://arxiv.org/pdf/1907.12333v1

  5. Refined inequalities for loosely trapped surface/attractive gravity probe surface

    Kangjae Lee, Tetsuya Shiromizu, Keisuke Izumi

      Vol. 105 ( 4 )   2022.2

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    Language:Japanese  

    We reexamine a loosely trapped surface (LTS) proposed as an indicator for
    strong gravity and an attractive gravity probe surface (AGPS) as that for
    gravity. Refined inequalities for them are derived by taking account of angular
    momentum, gravitational waves and matters.

    DOI: 10.1103/PhysRevD.105.044037

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/2111.08237v1

  6. Invertibility conditions for field transformations with derivatives: toward extensions of disformal transformation with higher derivatives

    Eugeny Babichev, Keisuke Izumi, Norihiro Tanahashi, Masahide Yamaguchi

      Vol. 2022 ( 1 )   2022.1

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    Language:Japanese  

    We discuss a field transformation from fields $\psi_a$ to other fields
    $\phi_i$ that involves derivatives, $\phi_i = \bar \phi_i(\psi_a,
    \partial_\alpha \psi_a, \ldots ;x^\mu)$, and derive conditions for this
    transformation to be invertible, primarily focusing on the simplest case that
    the transformation maps between a pair of two fields and involves up to their
    first derivatives. General field transformation of this type changes number of
    degrees of freedom, hence for the transformation to be invertible, it must
    satisfy certain degeneracy conditions so that additional degrees of freedom do
    not appear. Our derivation of necessary and sufficient conditions for
    invertible transformation is based on the method of characteristics, which is
    used to count the number of independent solutions of a given differential
    equation. As applications of the invertibility conditions, we show some
    non-trivial examples of the invertible field transformations with derivatives,
    and also give a rigorous proof that a simple extension of the disformal
    transformation involving a second derivative of the scalar field is not
    invertible.

    DOI: 10.1093/ptep/ptab151

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/2109.00912v2

  7. Asymptotic behavior of null geodesics near future null infinity II: curvatures, photon surface and dynamically transversely trapping surface

    Masaya Amo, Tetsuya Shiromizu, Keisuke Izumi, Hirotaka Yoshino, Yoshimune Tomikawa

        2021.10

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    Bearing in mind our previous study on asymptotic behavior of null geodesics
    near future null infinity, we analyze the behavior of geometrical quantities
    such as a certain extrinsic curvature and Riemann tensor in the Bondi
    coordinates. In the sense of asymptotics, the condition for an $r$-constant
    hypersurface to be a photon surface is shown to be controlled by a key quantity
    that determines the fate of photons initially emitted in angular directions. As
    a consequence, in four dimensions, such a non-expanding photon surface can be
    realized even near future null infinity in the presence of enormous energy flux
    for a short period of time. By contrast, in higher-dimensional cases, no such a
    photon surface can exist. This result also implies that the dynamically
    transversely trapping surface, which is proposed as an extension of a photon
    surface, can have an arbitrarily large radius in four dimensions.

    arXiv

    Other Link: http://arxiv.org/pdf/2110.10917v1

  8. Asymptotic behavior of null geodesics near future null infinity: Significance of gravitational waves

    Masaya Amo, Keisuke Izumi, Yoshimune Tomikawa, Hirotaka Yoshino, Tetsuya Shiromizu

      Vol. 104 ( 6 )   2021.9

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    Language:Japanese  

    We investigate the behavior of null geodesics near future null infinity in
    asymptotically flat spacetimes. In particular, we focus on the asymptotic
    behavior of null geodesics that correspond to worldlines of photons initially
    emitted in the directions tangential to the constant radial surfaces in the
    Bondi coordinates. The analysis is performed for general dimensions, and the
    difference between the four-dimensional cases and the higher-dimensional cases
    is stressed. In four dimensions, some assumptions are required to guarantee the
    null geodesics to reach future null infinity, in addition to the conditions of
    asymptotic flatness. Without these assumptions, gravitational waves may prevent
    photons from reaching null infinity. In higher dimensions, by contrast, such
    assumptions are not necessary, and gravitational waves do not affect the
    asymptotic behavior of null geodesics.

    DOI: 10.1103/PhysRevD.104.064025

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/2106.03150v3

  9. Divergence equations and uniqueness theorem of static spacetimes with conformal scalar hair

    Takeshi Shinohara, Yoshimune Tomikawa, Keisuke Izumi, Tetsuya Shiromizu

      Vol. 2021 ( 9 )   2021.9

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    Language:Japanese  

    We reexamine the Israel-type proof of the uniqueness theorem of the static
    spacetime outside the photon surface in the Einstein-conformal scalar system.
    We derive in a systematic fashion a new divergence identity which plays a key
    role in the proof. Our divergence identity includes three parameters, allowing
    us to give a new proof of the uniqueness.

    DOI: 10.1093/ptep/ptab107

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/2107.13133v1

  10. On uniqueness of static spacetime with conformal scalar in higher dimensions

    Keisuke Izumi, Yoshimune Tomikawa, Tetsuya Shiromizu

        2021.8

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    We discuss the uniqueness of asymptotically flat and static spacetimes in the
    $n$-dimensional Einstein-conformal scalar system. This theory potentially has a
    singular point in the field equations where the effective Newton constant
    diverges. We will show that the static spacetime with the conformal scalar
    field outside a certain surface $S_p$ associated with the singular point is
    unique.

    DOI: 10.1103/PhysRevD.104.104025

    arXiv

    Other Link: http://arxiv.org/pdf/2108.02588v1

  11. Area bound for surfaces in generic gravitational field

    Izumi Keisuke, Tomikawa Yoshimune, Shiromizu Tetsuya, Yoshino Hirotaka

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   Vol. 2021 ( 8 )   2021.8

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    Language:Japanese  

    DOI: 10.1093/ptep/ptab089

    Web of Science

  12. Perturbative S-matrix unitarity (S*S=1) in R-mu nu(2) gravity

    Abe Yugo, Inami Takeo, Izumi Keisuke

    MODERN PHYSICS LETTERS A   Vol. 36 ( 16 )   2021.5

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    Language:Japanese  

    DOI: 10.1142/S0217732321501054

    Web of Science

  13. Holographic entanglement entropy of a de Sitter braneworld with Lovelock terms

    Kushihara Kouki, Izumi Keisuke, Shiromizu Tetsuya

    PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS   Vol. 2021 ( 4 )   2021.4

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    Language:Japanese  

    DOI: 10.1093/ptep/ptab038

    Web of Science

  14. Holographic entanglement entropy of deSitter braneworld with Lovelock

    Kouki Kushihara, Keisuke Izumi, Tetsuya Shiromizu

        2021.2

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    We examine the deSitter entropy in the braneworld model with the
    Gauss-Bonnet/Lovelock terms. Then, we can see that the deSitter entropy
    computed through the Euclidean action exactly coincides with the holographic
    entanglement entropy.

    arXiv

    Other Link: http://arxiv.org/pdf/2102.12597v1

  15. Area bound for surfaces in generic gravitational field

    Keisuke Izumi, Yoshimune Tomikawa, Tetsuya Shiromizu, Hirotaka Yoshino

        2021.1

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    We define an attractive gravity probe surface (AGPS) as a compact 2-surface
    $S_\alpha$ with positive mean curvature $k$ satisfying $r^a D_a k / k^2 \ge
    \alpha$ (for a constant $\alpha>-1/2$) in the local inverse mean curvature
    flow, where $r^a D_a k$ is the derivative of $k$ in the outward unit normal
    direction. For asymptotically flat spaces, any AGPS is proved to satisfy the
    areal inequality $A_\alpha \le 4\pi [ ( 3+4\alpha)/(1+2\alpha) ]^2(Gm)^2$,
    where $A_{\alpha}$ is the area of $S_\alpha$ and $m$ is Arnowitt-Deser-Misner
    (ADM) mass. Equality is realized when the space is isometric to the
    $t=$constant hypersurface of the Schwarzschild spacetime and $S_\alpha$ is an
    $r=\mathrm{constant}$ surface with $r^a D_a k / k^2 = \alpha$. We adapt the two
    methods, the inverse mean curvature flow and the conformal flow. Therefore, our
    result is applicable to the case where $S_\alpha$ has multiple components. For
    anti-de Sitter (AdS) spaces, the similar inequality is derived, but the proof
    is performed only by using the inverse mean curvature flow. We also discuss the
    cases with asymptotically locally AdS spaces.

    arXiv

    Other Link: http://arxiv.org/pdf/2101.03860v1

  16. Invertible field transformations with derivatives: necessary and sufficient conditions

    Babichev Eugeny, Izumi Keisuke, Tanahashi Norihiro, Yamaguchi Masahide

    ADVANCES IN THEORETICAL AND MATHEMATICAL PHYSICS   Vol. 25 ( 2 ) page: 309 - 325   2021

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    Language:Japanese  

    Web of Science

  17. Perturbative $S$-matrix unitarity ($S^{\dagger}S=1$) in $R_{μν} ^2$ gravity

    Yugo Abe, Takeo Inami, Keisuke Izumi

        2020.12

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    We show that in the quadratic curvature theory of gravity, or simply $R_{\mu
    \nu} ^2$ gravity, the tree-level unitariy bound (tree unitarity) is violated in
    the UV region but an analog for $S$-matrix unitarity ($SS^{\dagger} = 1$) is
    satisfied. This theory is renormalizable, and hence the failure of tree
    unitarity is a counter example of Llewellyn Smith's conjecture on the relation
    between them. We have recently proposed a new conjecture that $S$-matrix
    unitarity gives the same conditions as renormalizability. We verify that
    $S$-matrix unitarity holds in the matter-graviton scattering at tree level in
    the $R_{\mu \nu} ^2$ gravity, demonstrating our new conjecture.

    arXiv

    Other Link: http://arxiv.org/pdf/2012.01717v3

  18. Loosely trapped surface and dynamically transversely trapping surface in Einstein-Maxwell systems Reviewed International journal

    Lee Kangjae, Shiromizu Tetsuya, Yoshino Hirotaka, Izumi Keisuke, Tomikawa Yoshimune

      Vol. 2020 ( 10 )   2020.10

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    DOI: 10.1093/ptep/ptaa133

    Web of Science

  19. Formation of dynamically transversely trapping surfaces and the stretched hoop conjecture Reviewed International journal

    Hirotaka Yoshino, Keisuke Izumi, Tetsuya Shiromizu, Yoshimune Tomikawa

    Prog. Theor. Exp. Phys. (2020) 053E01   Vol. 2020 ( 5 )   2020.5

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    A dynamically transversely trapping surface (DTTS) is a new concept of an
    extension of a photon sphere that appropriately represents a strong gravity
    region and has close analogy with a trapped surface. We study formation of a
    marginally DTTS in time-symmetric, conformally flat initial data with two black
    holes, with a spindle-shaped source, and with a ring-shaped source, and clarify
    that $\mathcal{C}\lesssim 6\pi GM$ describes the condition for the DTTS
    formation well, where $\mathcal{C}$ is the circumference and $M$ is the mass of
    the system. This indicates that an understanding analogous to the hoop
    conjecture for the horizon formation is possible. Exploring the ring system
    further, we find configurations where a marginally DTTS with the torus topology
    forms inside a marginally DTTS with the spherical topology, without being
    hidden by an apparent horizon. There also exist configurations where a
    marginally trapped surface with the torus topology forms inside a marginally
    trapped surface with the spherical topology, showing a further similarity
    between DTTSs and trapped surfaces.

    DOI: 10.1093/ptep/ptaa050

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1911.09893v2

  20. Transversely trapping surfaces: Dynamical version Reviewed International journal

    Hirotaka Yoshino, Keisuke Izumi, Tetsuya Shiromizu, Yoshimune Tomikawa

    Prog. Theor. Exp. Phys. (2020) 023E02   Vol. 2020 ( 2 )   2020.2

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    We propose new concepts, a dynamically transversely trapping surface (DTTS)
    and a marginally DTTS, as indicators for a strong gravity region. A DTTS is
    defined as a two-dimensional closed surface on a spacelike hypersurface such
    that photons emitted from arbitrary points on it in transverse directions are
    acceleratedly contracted in time, and a marginally DTTS is reduced to the
    photon sphere in spherically symmetric cases. (Marginally) DTTSs have a close
    analogy with (marginally) trapped surfaces in many aspects. After preparing the
    method of solving for a marginally DTTS in the time-symmetric initial data and
    the momentarily stationary axisymmetric initial data, some examples of
    marginally DTTSs are numerically constructed for systems of two black holes in
    the Brill-Lindquist initial data and in the Majumdar-Papapetrou spacetimes.
    Furthermore, the area of a DTTS is proved to satisfy the Penrose-like
    inequality, $A_0\le 4\pi (3GM)^2$, under some assumptions. Differences and
    connections between a DTTS and the other two concepts proposed by us
    previously, a loosely trapped surface [arXiv:1701.00564] and a
    static/stationary transversely trapping surface [arXiv:1704.04637], are also
    discussed. A (marginally) DTTS provides us with a theoretical tool to
    significantly advance our understanding of strong gravity fields. Also, since
    DTTSs are located outside the event horizon, they could possibly be related
    with future observations of strong gravity regions in dynamical evolutions.

    DOI: 10.1093/ptep/ptz161

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1909.08420v2

  21. S-matrix Unitarity and Renormalizability in Higher Derivative Theories Reviewed International journal

    Yugo Abe, Takeo Inami, Keisuke Izumi, Tomotaka Kitamura, Toshifumi Noumi

    Prog Theor Exp Phys (2019)   Vol. 2019 ( 8 )   2019.8

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    Language:Japanese   Publishing type:Research paper (scientific journal)  

    We investigate the relation between the $S$-matrix unitarity
    ($SS^{\dagger}=1$) and the renormalizability, in theories with negative norm
    states. The relation has been confirmed in many theories, such as gauge
    theories, Einstein gravity and Lifshitz-type non-relativistic theories by
    analyzing the unitarity bound, which follows from the $S$-matrix unitarity and
    the norm positivity. On the other hand, renormalizable theories with a higher
    derivative kinetic term do not necessarily satisfy the unitarity bound
    essentially because the unitarity bound does not hold due to the negative norm
    states. In these theories, it is not clear if the $S$-matrix unitarity provides
    a nontrivial constraint related to the renormalizability. In this paper we
    introduce scalar field models with a higher derivative kinetic term and analyze
    the $S$-matrix unitarity. We have positive results of the relation.

    DOI: 10.1093/ptep/ptz084

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1805.00262v1

  22. Divergence equations and uniqueness theorem of static black holes Reviewed International journal

    Masato Nozawa, Tetsuya Shiromizu, Keisuke Izumi, Sumio Yamada

    Classical and Quantum Gravity   Vol. 35 ( 17 )   2018.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    Equations of divergence type in static spacetimes play a significant role in
    the proof of uniqueness theorems of black holes. We generalize the divergence
    equation originally discovered by Robinson in four dimensional vacuum
    spacetimes into several directions. We find that the deviation from spherical
    symmetry is encoded in a symmetric trace-free tensor $H_{ij}$ on a static
    timeslice. This tensor is the crux for the construction of the desired
    divergence equation, which allows us to conclude the uniqueness of the
    Schwarzschild black hole without using Smarr's integration mass formula. In
    Einstein-Maxwell(-dilaton) theory, we apply the maximal principle for a number
    of divergence equations to prove the uniqueness theorem of static black holes.
    In higher $(n\ge 5)$ dimensional vacuum spacetimes, a central obstruction for
    applicability of the current proof is the integration of the
    $(n-2)$-dimensional scalar curvature over the horizon cross-section, which has
    been evaluated to be a topological constant by the Gauss-Bonnet theorem for
    $n=4$. Nevertheless, it turns out that the $(n-1)$-dimensional symmetric and
    traceless tensor $H_{ij}$ is still instrumental for the modification of the
    uniqueness proof based upon the positive mass theorem, as well as for the
    derivation of the Penrose-type inequality.

    DOI: 10.1088/1361-6382/aad206

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1805.11385v2

  23. Matter scattering in $R_{μν}^2$ gravity and unitarity Reviewed International journal

    Yugo Abe, Takeo Inami, Keisuke Izumi, Tomotaka Kitamura

    Prog Theor Exp Phys (2018)   Vol. 2018 ( 3 )   2018.3

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    Language:English   Publishing type:Research paper (scientific journal)  

    We investigate the ultraviolet (UV) behavior of two-scalar elastic scattering
    with graviton exchanges in higher curvature gravity theory. In the Einstein
    gravity, matter scattering is shown not to satisfy tree unitarity at high
    energy. Among a few possible directions to cure unitarity (i.e. UV completion
    of Einstein gravity), string theory, modified gravity, inclusion of
    high-mass/high-spin states, we take $R_{\mu\nu}^2$ gravity coupled to matter.
    We show that the matter scattering with graviton interactions satisfies the
    unitarity bound at high energy, in contrast with the Einstein gravity. The
    difference in unitarity property of the two gravity theories is due to that in
    the UV behavior of the propagator and is probably connected to that in another
    UV property, namely renormalizability property of the two.

    DOI: 10.1093/ptep/pty010

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1712.06305v2

  24. On uniqueness of static spacetimes with non-trivial conformal scalar field Reviewed International journal

    Yoshimune Tomikawa, Tetsuya Shiromizu, Keisuke Izumi

    Classical and Quantum Gravity   Vol. 34 ( 15 )   2017.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

    We discuss the uniqueness of the static spacetimes with non-trivial conformal
    scalar field. Then, we can show that the spacetime is unique to be the
    Bocharova-Bronnikov-Melnikov-Bekenstein solution outside the surface composed
    of the unstable circular orbit of photon(photon surface). In addition, we see
    that multi-photon surfaces having the same scalar field values do not exist.

    DOI: 10.1088/1361-6382/aa7906

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1702.05682v2

  25. Extension of photon surfaces and their area: Static and stationary spacetimes Reviewed International journal

    Hirotaka Yoshino, Keisuke Izumi, Tetsuya Shiromizu, Yoshimune Tomikawa

    Progress of Theoretical and Experimental Physics   Vol. 2017 ( 6 )   2017.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:OXFORD UNIV PRESS INC  

    We propose a new concept, the transversely trapping surface (TTS), as an
    extension of the static photon surface characterizing the strong gravity region
    of a static/stationary spacetime in terms of photon behavior. The TTS is
    defined as a static/stationary timelike surface $S$ whose spatial section is a
    closed two-surface, such that arbitrary photons emitted tangentially to $S$
    from arbitrary points on $S$ propagate on or toward the inside of $S$. We study
    the properties of TTSs for static spacetimes and axisymmetric stationary
    spacetimes. In particular, the area $A_0$ of a TTS is proved to be bounded as
    $A_0\le 4\pi(3GM)^2$ under certain conditions, where $G$ is the Newton constant
    and $M$ is the total mass. The connection between the TTS and the loosely
    trapped surface proposed by us [arXiv:1701.00564] is also examined.

    DOI: 10.1093/ptep/ptx072

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1704.04637v2

  26. On uniqueness of static black hole with conformal scalar hair Reviewed International journal

    Yoshimune Tomikawa, Tetsuya Shiromizu, Keisuke Izumi

    Progress of Theoretical and Experimental Physics   Vol. 2017 ( 3 )   2017.3

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    Language:English   Publishing type:Research paper (scientific journal)  

    We discuss the uniqueness of the static black hole in the Einstein gravity
    with a conformally coupled scalar field. In particular, we prove the uniqueness
    of the region outside of the photon surface, not event horizon.

    DOI: 10.1093/ptep/ptx033

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1612.01228v3

  27. Area bound for a surface in a strong gravity region Reviewed International journal

    Tetsuya Shiromizu, Yoshimune Tomikawa, Keisuke Izumi, Hirotaka Yoshino

    Progress of Theoretical and Experimental Physics   Vol. 2017 ( 3 )   2017.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:OXFORD UNIV PRESS INC  

    For asymptotically flat spacetimes, using the inverse mean curvature flow, we
    show that any compact $2$-surface, $S_0$, whose mean curvature and its
    derivative for outward direction are positive in spacelike hypersurface with
    non-negative Ricci scalar satisfies the inequality $A_0 \leq 4 \pi (3Gm)^2$,
    where $A_0$ is the area of $S_0$ and $m$ is the total mass. The upper bound is
    realized when $S_0$ is the photon sphere in a hypersurface isometric to
    $t=$const. slice of the Schwarzschild spacetime.

    DOI: 10.1093/ptep/ptx022

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1701.00564v2

  28. Hydro-elastic Complementarity in Black Branes at large D Reviewed International journal

    Roberto Emparan, Keisuke Izumi, Raimon Luna, Ryotaku Suzuki, Kentaro Tanabe

    Journal of High Energy Physics   ( 6 )   2016.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    We obtain the effective theory for the non-linear dynamics of black
    branes---both neutral and charged, in asymptotically flat or Anti-deSitter
    spacetimes---to leading order in the inverse-dimensional expansion. We find
    that black branes evolve as viscous fluids, but when they settle down they are
    more naturally viewed as solutions of an elastic soap-bubble theory. The two
    views are complementary: the same variable is regarded in one case as the
    energy density of the fluid, in the other as the deformation of the elastic
    membrane. The large-D theory captures finite-wavelength phenomena beyond the
    conventional reach of hydrodynamics. For asymptotically flat charged black
    branes (either Reissner-Nordstrom or p-brane-charged black branes) it yields
    the non-linear evolution of the Gregory-Laflamme instability at large D and its
    endpoint at stable non-uniform black branes. For Reissner-Nordstrom AdS black
    branes we find that sound perturbations do not propagate (have purely imaginary
    frequency) when their wavelength is below a certain charge-dependent value. We
    also study the polarization of black branes induced by an external electric
    field.

    DOI: 10.1007/JHEP06(2016)117

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1602.05752v3

  29. Tree-Unitarity and renormalizability in Lifshitz-scaling theory -- as a toy model of Hořava's gravity theory Reviewed

    Toshiaki Fujimori, Takeo Inami, Keisuke Izumi, Tomotaka Kitamura

        2016.1

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    We study tree-unitarity and renormalizability in Lifshitz-scaling theory,
    which is characterized by an anisotropic scaling between the spacial and time
    directions. Due to the lack of the Lorentz symmetry, the conditions for both
    unitarity and renormalizability are modified from those in relativistic
    theories. For renormalizability, the conventional discussion of the power
    counting conditions has to be extended. Because of the dependence of $S$-matrix
    elements on the reference frame, unitarity requires stronger conditions than
    those in relativistic cases. We show that the conditions for unitarity and
    renormalizabilty are identical as in relativistic theories. We discuss the
    importance of symmetries for a theory to be renormalizable.

    DOI: 10.1142/9789813203952_0054

    arXiv

    Other Link: http://arxiv.org/pdf/1601.06470v1

  30. Tree-Level Unitarity and Renormalizability in Lifshitz Scalar Theory Reviewed International journal

    Toshiaki Fujimori, Takeo Inami, Keisuke Izumi, Tomotaka Kitamura

    Progress of Theoretical and Experimental Physics   ( 1 )   2015.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:OXFORD UNIV PRESS INC  

    We study unitarity and renormalizability in the Lifshitz scalar field theory,
    which is characterized by an anisotropic scaling between the space and time
    directions. Without the Lorentz symmetry, both the unitarity and the
    renormalizability conditions are modified from those in relativistic theories.
    We show that for renormalizability, an extended version of the power counting
    condition is required in addition to the conventional one. The unitarity bound
    for S-matrix elements also gives stronger constraints on interaction terms
    because of the reference frame dependence of scattering amplitudes. We prove
    that both unitarity and renormalizability require identical conditions as in
    the case of conventional relativistic theories.

    DOI: 10.1093/ptep/ptv185

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1510.07237v1

  31. Boundary effect of anomaly-induced action (vol 92, 024035, 2015) Reviewed

    Che-Min Shen, Keisuke Izumi, Pisin Chen

    PHYSICAL REVIEW D   Vol. 92 ( 4 )   2015.8

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    DOI: 10.1103/PhysRevD.92.049902

    Web of Science

  32. Boundary effect of anomaly-induced action Reviewed

    Che-Min Shen, Keisuke Izumi, Pisin Chen

    PHYSICAL REVIEW D   Vol. 92 ( 2 )   2015.7

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    We discuss the boundary effect of anomaly-induced action in two-dimensional spacetime, which is ignored in previous studies. Anomaly-induced action, which gives the stress tensor with the same trace as the trace anomaly, can be represented in terms of local operators by introducing an auxiliary scalar field. Although the degrees of freedom of the auxiliary field can in principle describe the quantum states of the original field, the principal relation between them was unclear. We show here that, by considering the boundary effect, the solutions of classical auxiliary fields are naturally related to the quantum states of the original field. We demonstrate this conclusion via several examples such as the flat, black hole, and the de Sitter spacetime.

    DOI: 10.1103/PhysRevD.92.024035

    Web of Science

    arXiv

  33. Power-counting and renormalizability in Lifshitz scalar theory Reviewed International journal

    Keisuke Izumi

    Physical Review D   Vol. 91 ( 12 )   2015.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We study the renormalizability in theories of a self-interacting Lifshitz
    scalar field. We show that although the statement of power-counting is true at
    one-loop order, in generic cases where the scalar field is dimensionless, an
    infinite number of counter terms are involved in the renormalization procedure.
    This problem can be avoided by imposing symmetries, the shift symmetry in the
    present paper, which allow only a finite number of counter terms to appear. The
    symmetry requirements might have important implications for the construction of
    matter field sectors in the Horava-Lifshitz gravity.

    DOI: 10.1103/physrevd.91.125007

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1502.01820v1

  34. Ghosts in the self-accelerating DGP branch with Gauss–Bonnet effect Reviewed International journal

    Keisuke Izumi

    The European Physical Journal C   Vol. 75 ( 6 )   2015.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:SPRINGER  

    The Dvali-Gabadadze-Porrati brane-world model provides a possible approach to
    address the late-time cosmic acceleration. However, it has subsequently been
    pointed out that a ghost instability will arise on the self-accelerating
    branch. Here, we carefully investigate whether this ghost problem could be
    possibly cured by introducing the Gauss-Bonnet term in the five-dimensional
    bulk action, a natural generalization to the Dvali-Gabadadze-Porrati model. Our
    analysis is carried out for a background where a de Sitter brane is embedded in
    an anti-de Sitter bulk. Our result shows that the ghost excitations cannot be
    avoided even in this modified model.

    DOI: 10.1140/epjc/s10052-015-3463-0

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1405.0850v2

  35. New definition of a wormhole throat Reviewed International journal

    Yoshimune Tomikawa, Keisuke Izumi, Tetsuya Shiromizu

    PHYSICAL REVIEW D   Vol. 91 ( 10 )   2015.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We present a new definition of the wormhole throat including the flare-out condition and the feature corresponding to the traversability for general dynamical spacetimes in terms of null geodesic congruences. We will examine our definition for some examples and see advantages compared to the others.

    DOI: 10.1103/PhysRevD.91.104008

    Web of Science

    arXiv

  36. The boundary effect of anomaly-induced action Reviewed

    Che-Min Shen, Keisuke Izumi, Pisin Chen

    Physical Review D     2015.5

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    Language:English   Publishing type:Research paper (scientific journal)  

    We discuss the boundary effect of anomaly-induced action in two-dimensional
    spacetime, which is ignored in previous studies. Anomaly-induced action, which
    gives the stress tensor with the same trace as the trace anomaly, can be
    represented in terms of local operators by introducing an auxiliary scalar
    field. Although the degrees of freedom of the auxiliary field can in principle
    describe the quantum states of the original field, the principal relation
    between them was unclear. We show here that, by considering the boundary
    effect, the solutions of classical auxiliary fields are naturally related to
    the quantum states of the original field. We demonstrate this conclusion via
    several examples such as the flat, black hole and the de Sitter spacetime.

    DOI: 10.1103/PhysRevD.92.024035

    arXiv

    Other Link: http://arxiv.org/pdf/1505.00959v1

  37. Problems of massive gravities Reviewed International journal

    S. Deser, K. Izumi, Y. C. Ong, A. Waldron

    MODERN PHYSICS LETTERS A   Vol. 30 ( 3-4 )   2015.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:WORLD SCIENTIFIC PUBL CO PTE LTD  

    The method of characteristics is a key tool for studying consistency of equations of motion; it allows issues such as predictability, maximal propagation speed, superluminality, unitarity and acausality to be addressed without requiring explicit solutions. We review this method and its application to massive gravity (mGR) theories to show the limitations of these models' physical viability: Among their problems are loss of unique evolution, superluminal signals, matter coupling inconsistencies and micro-acausality (propagation of signals around local closed time-like curves (CTCs)/closed causal curves (CCCs)). We extend previous no-go results to the entire three-parameter range of mGR theories. It is also argued that bimetric models suffer a similar fate.

    DOI: 10.1142/S0217732315400064

    Web of Science

    arXiv

  38. Boundary effect of anomaly-induced action Reviewed International journal

    Che-Min Shen, Keisuke Izumi, Pisin Chen

    Physical Review D     2015

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1103/PhysRevD.92.049902, 10.1103/PhysRevD.92.024035

  39. Remnant Symmetry, Propagation and Evolution in f(T) Gravity Reviewed International journal

    Pisin Chen, Keisuke Izumi, James M. Nester, Yen Chin Ong

    PHYSICAL REVIEW D   Vol. 91 ( 6 )   2014.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    It was recently argued that f(T) gravity could inherit "remnant symmetry"
    from the full Lorentz group, despite the fact that the theory is not locally
    Lorentz invariant. Confusion has arisen regarding the implication of this
    result for the previous works, which established that f(T) gravity is
    pathological due to superluminal propagation, local acausality, and non-unique
    time evolution. We clarify that the existence of the "remnant group" does not
    rid the theory of these various problems, but instead strongly supports it.

    DOI: 10.1103/PhysRevD.91.064003

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1412.8383v3

  40. Wormhole on DGP brane Reviewed International journal

    Yoshimune Tomikawa, Tetsuya Shiromizu, Keisuke Izumi

    PHYSICAL REVIEW D   Vol. 90 ( 12 )   2014.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We analyze a spacetime structure on a new brane configuration constructed
    recently in the Dvali-Gabadadze-Porrati braneworld context. The brane, embedded
    on a five-dimensional bubble of nothing, has a wormhole structure. It is an
    exact solution without any matter fields, and thus the energy conditions for
    matter fields are trivially satisfied. We see that, under the traversability
    condition, the size of the bubble should be larger than 10^{10}cm or so.

    DOI: 10.1103/PhysRevD.90.126001

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1409.6816v2

  41. DGP braneworld with a bubble of nothing Reviewed International journal

    Keisuke Izumi, Tetsuya Shiromizu

    PHYSICAL REVIEW D   Vol. 90 ( 4 )   2014.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We construct exact solutions with the bubble of nothing in the Dvali-Gabadadze-Porrati braneworld model. The configuration with a single brane can be constructed, unlike in the Randall-Sundrum braneworld model. The geometry on the single brane looks like the Einstein-Rosen bridge. We also discuss the junction of multibranes. Surprisingly, even without any artificial matter fields on the branes such as three-dimensional tension of the codimension-two objects, two branes can be connected in certain configurations. We investigate solutions of multibranes too. The presence of solutions may indicate the semiclassical instability of the models.

    DOI: 10.1103/PhysRevD.90.046005

    Web of Science

    arXiv

  42. Causal structures in Gauss-Bonnet gravity Reviewed International journal

    Keisuke Izumi

    Physical Review D     2014.8

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    Language:English   Publishing type:Research paper (scientific journal)  

    We analyze causal structures in Gauss-Bonnet gravity. It is known that
    Gauss-Bonnet gravity potentially has superluminal propagation of gravitons due
    to its noncanonical kinetic terms. In a theory with superluminal modes, an
    analysis of causality based on null curves makes no sense, and thus, we need to
    analyze them in a different way. In this paper, using the method of the
    characteristics, we analyze the causal structure in Gauss-Bonnet gravity. We
    have the result that, on a Killing horizon, gravitons can propagate in the null
    direction tangent to the Killing horizon. Therefore, a Killing horizon can be a
    causal edge as in the case of general relativity, i.e. a Killing horizon is the
    "event horizon" in the sense of causality. We also analyze causal structures on
    nonstationary solutions with $(D-2)$-dimensional maximal symmetry, including
    spherically symmetric and flat spaces. If the geometrical null energy
    condition, $R_{AB}N^AN^B \ge 0$ for any null vector $N^A$, is satisfied, the
    radial velocity of gravitons must be less than or equal to that of light.
    However, if the geometrical null energy condition is violated, gravitons can
    propagate faster than light. Hence, on an evaporating black hole where the
    geometrical null energy condition is expected not to hold, classical gravitons
    can escape from the "black hole" defined with null curves. That is, the causal
    structures become nontrivial. It may be one of the possible solutions for the
    information loss paradox of evaporating black holes.

    DOI: 10.1103/physrevd.90.044037

    arXiv

    Other Link: http://arxiv.org/pdf/1406.0677v2

  43. Superluminal Propagation and Acausality of Nonlinear Massive Gravity Reviewed

    S. Deser, K. Izumi, Y. C. Ong, A. Waldron

        2013.12

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    Massive gravity is an old idea: trading geometry for mass. Much effort has<br />
    been expended on establishing a healthy model, culminating in the current<br />
    ghost-free version. We summarize here our recent findings -- that it is still<br />
    untenable -- because it is locally acausal: CTC solutions can be constructed in<br />
    a small neighborhood of any event.

    DOI: 10.1142/9789814590112_0029

    arXiv

  44. Massive gravity acausality redux Reviewed International journal

    S. Deser, K. Izumi, Y.C. Ong, A. Waldron

    Physics Letters B   Vol. 726 ( 1-3 ) page: 544 - 548   2013.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    Massive gravity (mGR) is a 5(= 2s + 1) degree of freedom, finite range extension of GR. However, amongst other problems, it is plagued by superluminal propagation, first uncovered via a second order shock analysis. First order mGR shock structures have also been studied, but the existence of superluminal propagation in that context was left open. We present here a concordance of these methods, by an explicit (first order) characteristic matrix computation, which confirms mGR's superluminal propagation as well as acausality. (C) 2013 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physletb.2013.09.001

    Web of Science

    arXiv

  45. Acausality and Nonunique Evolution in Generalized Teleparallel Gravity Reviewed International journal

    Keisuke Izumi, Je-An Gu, Yen Chin Ong

    PHYSICAL REVIEW D   Vol. 89 ( 8 )   2013.9

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    We show the existence of physical superluminal modes and acausality in the
    Brans-Dicke type of extension of teleparallel gravity that includes F(T)
    gravity and teleparallel dark energy as special cases. We derive the
    characteristic hypersurface for the extra degrees of freedom in the theory,
    thereby showing that the time evolution is not unique and closed causal curves
    can appear. Furthermore, we present a concrete disastrous solution in Bianchi
    type I spacetime, in which the anisotropy in expansion can be any function of
    time, and thus anisotropy can emerge suddenly, a simple demonstration that the
    theory is physically problematic.

    DOI: 10.1103/PhysRevD.89.084025

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1309.6461v2

  46. Tensor Perturbations from Brane-World Inflation with Curvature Effects Reviewed International journal

    Mariam Bouhmadi-Lopez, Yen-Wei Liu, Keisuke Izumi, Pisin Chen

    PHYSICAL REVIEW D   Vol. 89 ( 6 )   2013.8

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    The brane-world scenario provides an intriguing possibility to explore the
    phenomenological cosmology implied by string/M theory. In this paper, we
    consider a modified Randall-Sundrum single brane model with two natural
    generalizations: a Gauss-Bonnet term in the five-dimensional bulk action as
    well as an induced gravity term in the four-dimensional brane action, which are
    the leading-order corrections to the Randall-Sundrum model. We study the
    influence of these combined effects on the evolution of the primordial
    gravitational waves generated during an extreme slow-roll inflation on the
    brane. The background, for the early inflationary era, is then modeled through
    a de Sitter brane embedded within an anti-de Sitter bulk. In this framework, we
    show that both effects tend to suppress the Randall-Sundrum enhancement of the
    amplitude of the tensor perturbations at relatively high energies. Moreover,
    the Gauss-Bonnet effect, relative to standard general relativity, will abruptly
    enhance the tensor-to-scalar ratio and break the standard consistency relation
    at high energies, which cannot be evaded by invoking the induced gravity
    effect, even though the induced gravity strength would mildly counterbalance
    these significant changes at high energies. We note that the brane-world model
    with or without the induced gravity effect fulfills the consistency relation.
    Finally, we discuss some implications of the observational constraints.

    DOI: 10.1103/PhysRevD.89.063501

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1308.5765v2

  47. Natural Emergence of Cosmological Constant and Dark Radiation from Stephenson-Kilmister-Yang-Camenzind Theory of Gravity Reviewed International journal

    Pisin Chen, Keisuke Izumi, Nien-En Tung

    Physical Review D   Vol. 88 ( 12 )   2013.4

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    We show that the Stephenson-Kilmister-Yang (SKY) equation combined with
    Camenzind's matter current term naturally provides the cosmological constant
    and dark radiation as integration constants of the SKYC field equation. To
    characterize the property of the dark radiation, we develop a method to
    separate it from the ordinary radiation. We found a special property of
    Camenzind's matter current, namely that the solution space for radiation in
    fact belongs to that of the vacuum solution of SKY equation. We also found that
    his matter current does not obey the conservation condition suggested by
    Kilmister. Finally, we discuss the possible role of dark radiation emergent
    from the SKYC theory in recent cosmic-microwave-background observations and its
    implications to the inflation scenario.

    DOI: 10.1103/PhysRevD.88.123006

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1304.6334v1

  48. An Analysis of Characteristics in Non-Linear Massive Gravity Reviewed International journal

    Keisuke Izumi, Yen Chin Ong

    Classical and Quantum Gravity     2013.3

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    We study the Cauchy problem in a special case of non-linear massive gravity:
    the two-tensor "f-g" theory. Despite being ghost-free, it has recently been
    argued that the theory is inherently problematic due to the existence of
    superluminal shock waves. Furthermore it is claimed that acausal characteristic
    can arise for any choice of background. In order to further understand the
    causal structure of the theory, we carefully perform a detailed analysis of the
    characteristic equations and show that the theory does admit a well-posed
    Cauchy problem, i.e., there exist hypersurfaces that are not characteristic
    hypersurface. Puzzles remain regarding the existence of a superluminal
    propagating mode in both the f-g theory, as well as in the full non-linear
    massive gravity. That is, our result should not be taken as any indication of
    the healthiness of the theory. We also give a detailed review of
    Cauchy-Kovalevskaya theorem and its application in the Appendix, which should
    be useful for investigating causal structures of other theories of gravity.

    DOI: 10.1088/0264-9381/30/18/184008

    arXiv

    Other Link: http://arxiv.org/pdf/1304.0211v2

  49. Problems with Propagation and Time Evolution in f(T) Gravity Reviewed International journal

    Yen Chin Ong, Keisuke Izumi, James M. Nester, Pisin Chen

    Physical Review D   Vol. 88 ( 2 )   2013.3

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    Teleparallel theories of gravity have a long history. They include a special
    case referred to as the Teleparallel Equivalent of General Relativity (TEGR,
    aka GR$_{\|}$). Recently this theory has been generalized to f(T) gravity.
    Tight constraints from observations suggest that f(T) gravity is not as robust
    as initially hoped. This might hint at hitherto undiscovered problems at the
    theoretical level. In this work, we point out that a generic f(T) theory can be
    expected to have certain problems including superluminal propagating modes, the
    presence of which can be revealed by using the characteristic equations that
    govern the dynamics in f(T) gravity and/or the Hamiltonian structure of the
    theory via Dirac constraint analysis. We use several examples from simpler
    gauge field theories to explain how such superluminal modes could arise. We
    also point out problems with the Cauchy development of a constant time
    hypersurface in FLRW spacetime in f(T) gravity. The time evolution from a FLRW
    (and as a special case, Minkowski spacetime) initial condition is not unique.

    DOI: 10.1103/PhysRevD.88.024019

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1303.0993v2

  50. Cosmological Perturbation in f(T) Gravity Revisited Reviewed International journal

    Keisuke Izumi, Yen Chin Ong

    Journal of Cosmology and Astroparticle Physics     2012.12

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    We perform detailed investigation of cosmological perturbations in f(T)
    theory of gravity coupled with scalar field. Our work emphasizes on the way to
    gauge fix the theory and we examine all possible modes of perturbations up to
    second order. The analysis includes pseudoscalar and pseudovector modes in
    addition to the usual scalar, vector, and tensor modes. We find no
    gravitational propagating degree of freedom in the scalar, pseudoscalar,
    vector, as well as pseudovector modes. In addition, we find that the scalar and
    tensor perturbations have exactly the same form as their counterparts in usual
    general relativity with scalar field, except that the factor of reduced Planck
    mass squared $M_{\text{pl } }^2 \equiv 1/(8\pi G)$ that occurs in the latter has
    now been replaced by an effective time-dependentgravitational coupling $-2
    (df/dT)|_{T=T_0}$, with $T_0$ being the background torsion scalar. The absence
    of extra degrees of freedom of f(T) gravity at second order linear perturbation
    indicates that f(T) gravity is highly nonlinear. Consequently one cannot
    conclusively analyze stability of the theory without performing nonlinear
    analysis that can reveal the propagation of the extra degrees of freedom.

    DOI: 10.1088/1475-7516/2013/06/029

    arXiv

    Other Link: http://arxiv.org/pdf/1212.5774v2

  51. Spherically symmetric analysis on open FLRW solution in non-linear massive gravity Reviewed International journal

    Chien-I Chiang, Keisuke Izumi, Pisin Chen

    Journal of Cosmology and Astroparticle Physics   ( 12 )   2012.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:IOP PUBLISHING LTD  

    We study non-linear massive gravity in the spherically symmetric context. Our
    main motivation is to investigate the effect of helicity-0 mode which remains
    elusive after analysis of cosmological perturbation around an open
    Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. The non-linear form of the
    effective energy-momentum tensor stemming from the mass term is derived for the
    spherically symmetric case. Only in the special case where the area of the two
    sphere is not deviated away from the FLRW universe, the effective energy
    momentum tensor becomes completely the same as that of cosmological constant.
    This opens a window for discriminating the non-linear massive gravity from
    general relativity (GR). Indeed, by further solving these spherically symmetric
    gravitational equations of motion in vacuum to the linear order, we obtain a
    solution which has an arbitrary time-dependent parameter. In GR, this parameter
    is a constant and corresponds to the mass of a star. Our result means that
    Birkhoff's theorem no longer holds in the non-linear massive gravity and
    suggests that energy can probably be emitted superluminously (with infinite
    speed) on the self-accelerating background by the helicity-0 mode, which could
    be a potential plague of this theory.

    DOI: 10.1088/1475-7516/2012/12/025

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1208.1222v2

  52. Trispectrum estimation in various models of equilateral type non-Gaussianity Reviewed International journal

    Keisuke Izumi, Shuntaro Mizuno, Kazuya Koyama

    Physical Review D   Vol. 85 ( 2 )   2011.9

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    We calculate the shape correlations between trispectra in various equilateral
    non-Gaussian models, including DBI inflation, ghost inflation and Lifshitz
    scalars, using the full trispectrum as well as the reduced trispectum. We find
    that most theoretical models are distinguishable from the shapes of primordial
    trispectra except for several exceptions where it is difficult to discriminate
    between the models, such as single field DBI inflation and a Lifshitz scalar
    model. We introduce an estimator for the amplitude of the trispectrum, $g_{\rm
    NL} ^{equil}$ and relate it to model parameters in various models. Using
    constraints on $g_{\rm NL} ^{equil}$ from WMAP5, we give constraints on the
    model parameters.

    DOI: 10.1103/PhysRevD.85.023521

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1109.3746v3

  53. Systematic solution-generation of five-dimensional black holes Reviewed International journal

    Hideo Iguchi, Keisuke Izumi, Takashi Mishima

    Progress of Theoretical Physics Supplement   ( 189 ) page: 93 - 125   2011.6

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    Solitonic solution-generating methods are powerful tools to construct
    nontrivial black hole solutions of the higher-dimensional Einstein equations
    systematically. In five dimensions particularly, the solitonic methods can be
    successfully applied to the construction of asymptotically Minkowski spacetimes
    with multiple horizons. We review the solitonic methods applicable to
    higher-dimensional vacuum spacetimes and present some five-dimensional examples
    derived from the methods.

    DOI: 10.1143/PTPS.189.93

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1106.0387v3

  54. Nonlinear superhorizon perturbations in Horava-Lifshitz gravity Reviewed International journal

    Keisuke Izumi, Shinji Mukohyama

    Physical Review D   Vol. 84 ( 6 )   2011.5

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    We perform a fully nonlinear analysis of superhorizon perturbation in
    Ho\v{r}ava-Lifshitz gravity, based on the gradient expansion method. We present
    a concrete expression for the solution of gravity equations up to the second
    order in the gradient expansion, and prove that the solution can be extended to
    any order. The result provides yet another example for analogue of the
    Vainshtein effect: the nonlinear solution is regular in the limit $\lambda\to
    1$ and recovers general relativity coupled to dark matter at low energy.
    Finally, we propose a definition of nonlinear curvature perturbation ${\cal R}$
    in Ho\v{r}ava-Lifshitz gravity and show that it is conserved up to the first
    order in the gradient expansion.

    DOI: 10.1103/PhysRevD.84.064025

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1105.0246v2

  55. Non-Gaussianity from Lifshitz Scalar Reviewed International journal

    Keisuke Izumi, Takeshi Kobayashi, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   ( 10 )   2010.8

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    A Lifshitz scalar with the dynamical critical exponent z = 3 obtains
    scale-invariant, super-horizon field fluctuations without the need of an
    inflationary era. Since this mechanism is due to the special scaling of the
    Lifshitz scalar and persists in the presence of unsuppressed self-couplings,
    the resulting fluctuation spectrum can deviate from a Gaussian distribution. We
    study the non-Gaussian nature of the Lifshitz scalar's intrinsic field
    fluctuations, and show that primordial curvature perturbations sourced from
    such field fluctuations can have large non-Gaussianity of order f_NL = O(100),
    which will be detected by upcoming CMB observations. We compute the bispectrum
    and trispectrum of the fluctuations, and discuss their configurations in
    momentum space. In particular, the bispectrum is found to take various shapes,
    including the local, equilateral, and orthogonal shapes. Intriguingly, all
    integrals in the in-in formalism can be performed analytically.

    DOI: 10.1088/1475-7516/2010/10/031

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1008.1406v2

  56. Trispectrum from Ghost Inflation Reviewed International journal

    Keisuke Izumi, Shinji Mukohyama

    Journal of Cosmology and Astroparticle Physics   ( 6 )   2010.4

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    Ghost inflation predicts almost scale-invariant primordial cosmological
    perturbations with relatively large non-Gaussianity. The bispectrum is known to
    have a large contribution at the wavenumbers forming an equilateral triangle
    and the corresponding nonlinear parameter $f_{NL}^{equil}$ is typically of
    order $O(10^2)$. In this paper we calculate trispectrum from ghost inflation
    and show that the corresponding nonlinear parameter $\tau_{NL}$ is typically of
    order $O(10^4)$. We investigate the shape dependence of the trispectrum and see
    that it has some features different from DBI inflation. Therefore, our result
    may be useful as a template to distinguish ghost inflation from other models of
    inflation by future experiments.

    DOI: 10.1088/1475-7516/2010/06/016

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/1004.1776v1

  57. Stellar center is dynamical in Horava-Lifshitz gravity Reviewed International journal

    Keisuke Izumi, Shinji Mukohyama

    Physical Review D   Vol. 81 ( 4 )   2009.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    In Horava-Lifshitz gravity, regularity of a solution requires smoothness of
    not only the spacetime geometry but also the foliation. As a result, the
    regularity condition at the center of a star is more restrictive than in
    general relativity. Assuming that the energy density is a piecewise-continuous,
    non-negative function of the pressure and that the pressure at the center is
    positive, we prove that the momentum conservation law is incompatible with the
    regularity at the center for any spherically-symmetric, static configurations.
    The proof is totally insensitive to the structure of higher spatial curvature
    terms and, thus, holds for any values of the dynamical critical exponent $z$.
    Therefore, we conclude that a spherically-symmetric star should include a
    time-dependent region near the center. We also comment on the condition under
    which linear instability of the scalar graviton does not show up.

    DOI: 10.1103/PhysRevD.81.044008

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/0911.1814v2

  58. Particle production in models with helicity-0 graviton ghost in de Sitter spacetime Reviewed International journal

    Keisuke Izumi, Takahiro Tanaka

    Progress of Theoretical Physics   Vol. 121 ( 2 ) page: 427 - 436   2008.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    We revisit the problem of the helicity-0 ghost mode of massive graviton in
    the de Sitter background. In general, the presence of a ghost particle, which
    has negative energy, drives the vacuum to be unstable through pair production
    of ghost particles and ordinary particles. In the case that the vacuum state
    preserves the de Sitter invariance, the number density created by the pair
    production inevitably diverges due to unsuppressed ultra-violet(UV)
    contributions. In such cases one can immediately conclude that the model is not
    viable. However, in the massive gravity theory we cannot construct a vacuum
    state which respects the de Sitter invariance. Therefore the presence of a
    ghost does not immediately mean the breakdown of the model. Explicitly
    estimating the number density and the energy density of particles created by
    the pair production of two conformal scalar particles and one helicity-0 ghost
    graviton, we find that these densities both diverge. However, since models with
    helicity-0 ghost graviton have no de Sitter invariant vacuum state, it is
    rather natural to consider a UV cutoff scale in the three-dimensional momentum
    space. Then, even if we take the cutoff scale as large as the Planck scale, the
    created number density and energy density are well suppressed. In many models
    the cutoff scale is smaller than the Planck scale. In such models the created
    number density and the energy density are negligiblly small as long as only the
    physics below the cutoff scale is concerned.

    DOI: 10.1143/PTP.121.427

    Scopus

    arXiv

    Other Link: http://arxiv.org/pdf/0810.4811v1

  59. Massive spin-2 ghost in de sitter spacetime

    K. Izumi, K. Koyama, O. Pujolas, T. Tanaka

    Proceedings of the 18th Workshop on General Relativity and Gravitation in Japan, JGRG 2008     2008

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    Language:English  

  60. Orthogonal black di-ring solution Reviewed International journal

    Keisuke Izumi

    Progress of Theoretical Physics   Vol. 119 ( 5 ) page: 757 - 774   2007.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    We construct a five dimensional exact solution of the orthogonal black
    di-ring which has two black rings whose $S^1$-rotating planes are orthogonal.
    This solution has four free parameters which represent radii of and speeds of
    $S^1$-rotation of the black rings. We use the inverse scattering method. This
    method needs the seed metric. We also present a systematic method how to
    construct a seed metric. Using this method, we can probably construct other
    solutions having many black rings on the two orthogonal planes with or without
    a black hole at the center.

    DOI: 10.1143/PTP.119.757

    Scopus

    arXiv

    Other Link: http://arxiv.org/pdf/0712.0902v3

  61. Bubbles in the self-accelerating universe Reviewed International journal

    Keisuke Izumi, Kazuya Koyama, Oriol Pujolàs, Takahiro Tanaka

    Physical Review D - Particles, Fields, Gravitation and Cosmology   Vol. 76 ( 10 )   2007.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    We revisit the issue of the stability in the Dvali-Gabadadze-Porrati model by considering the nucleation of bubbles of the conventional branch within the self-accelerating branch. We construct an instanton describing this process in the thin wall approximation. On one side of the bubble wall, the bulk consists of the exterior of the brane, while on the other side it is the interior. The solution requires the presence of a 2-brane (the bubble wall) which induces the transition. However, we show that this instanton cannot be realized as the thin wall limit of any smooth solution. Once the bubble thickness is resolved, the equations of motion do not allow O(4) symmetric solutions joining the two branches. We conclude that the thin wall instanton is unphysical, and that one cannot have processes connecting the two branches, unless negative tension bubble walls are introduced. This also suggests that the self-accelerating branch does not decay into the conventional branch nucleating bubbles. We comment on other kinds of bubbles that could interpolate between the two branches. © 2007 The American Physical Society.

    DOI: 10.1103/PhysRevD.76.104041

    Scopus

    arXiv

    Other Link: http://arxiv.org/pdf/0706.1980v1

  62. No de Sitter invariant vacuum in massive gravity theory with ghost Reviewed International journal

    Keisuke Izumi, Takahiro Tanaka

    Progress of Theoretical Physics   Vol. 121 ( 2 ) page: 419 - 426   2007.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    In this letter we point out that the massive gravity theory with a graviton
    ghost mode in de Sitter background cannot possess a de Sitter invariant vacuum
    state. In order to avoid a negative norm state, we must associate the creation
    operator of the ghost mode with a negative-energy mode function instead of a
    positive-energy one as the mode function. Namely, we have to adopt a different
    procedure of quantization for a ghost. When a theory has a symmetry mixing a
    ghost mode with ordinary non-ghost modes, the choice of a ghost mode is not
    unique. However, quantization of a ghost is impossible without specifying a
    choice of ghost mode, which breaks the symmetry. For this reason, the vacuum
    state cannot respect the symmetry. In the massive gravity theory with a
    graviton ghost mode in de Sitter background, the ghost is the helicity-0 mode
    of the graviton. This ghost mode is mixed with the other helicity graviton
    modes under the action of de Sitter symmetry. Therefore, there is no de Sitter
    invariant vacuum in such models. This leads to an interesting possibility that
    non-covariant cutoff of the low energy effective theory may naturally arise. As
    a result, the instability due to the pair production of a ghost and normal
    non-ghost particles gets much milder and that the model may escape from being
    rejected.

    DOI: 10.1143/PTP.121.419

    Scopus

    arXiv

    Other Link: http://arxiv.org/pdf/0709.0199v2

  63. Renormalized Newtonian Cosmic Evolution with Primordial Non-Gaussianity Reviewed International journal

    Keisuke Izumi, Jiro Soda

    Physical Review D   Vol. 76 ( 8 )   2007.6

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We study Newtonian cosmological perturbation theory from a field theoretical
    point of view. We derive a path integral representation for the cosmological
    evolution of stochastic fluctuations. Our main result is the closed form of the
    generating functional valid for any initial statistics. Moreover, we extend the
    renormalization group method proposed by Mataresse and Pietroni to the case of
    primordial non-Gaussian density and velocity fluctuations. As an application,
    we calculate the nonlinear propagator and examine how the non-Gaussianity
    affects the memory of cosmic fields to their initial conditions. It turns out
    that the non-Gaussianity affect the nonlinear propagator. In the case of
    positive skewness, the onset of the nonlinearity is advanced with a given
    comoving wavenumber. On the other hand, the negative skewness gives the
    opposite result.

    DOI: 10.1103/PhysRevD.76.083517

    Web of Science

    arXiv

    Other Link: http://arxiv.org/pdf/0706.1604v2

  64. Unexorcized ghost in DGP brane world Reviewed International journal

    Keisuke Izumi, Kazuya Koyama, Takahiro Tanaka

    Journal of High Energy Physics   Vol. 2007 ( 4 )   2006.10

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    Language:English   Publishing type:Research paper (scientific journal)  

    The braneworld model of Dvali-Gabadadze-Porrati realizes the
    self-accelerating universe. However, it is known that this cosmological
    solution contains a spin-2 ghost. We study the possibility of avoiding the
    appearance of the ghost by slightly modifying the model, introducing the second
    brane. First we consider a simple model without stabilization of the separation
    of the brane. By changing the separation between the branes, we find we can
    erase the spin-2 ghost. However, this can be done only at the expense of the
    appearance of a spin-0 ghost instead. We discuss why these two different types
    of ghosts are correlated. Then, we examine a model with stabilization of the
    brane separation. Even in this case, we find that the correlation between
    spin-0 and spin-2 ghosts remains. As a result we find we cannot avoid the
    appearance of ghost by two-branes model.

    DOI: 10.1088/1126-6708/2007/04/053

    Scopus

    arXiv

    Other Link: http://arxiv.org/pdf/hep-th/0610282v3

  65. The avoidance of the ghost problem in the DGP brane world: Two-branes model

    K. Izumi, T. Tanaka

    Proceedings of the 15th Workshop on General Relativity and Gravitation in Japan, JGRG 2005     page: 135 - 138   2005

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Presentations 46

  1. Area inequality in weak gravity region Invited International conference

    Keisuke Izumi

    Quantum extreme universe from quantum information  2022.9.30 

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    Event date: 2022.9

    Language:English   Presentation type:Oral presentation (invited, special)  

  2. 弱重力場における面積不等式

    泉圭介, 富川祥宗, 白水徹也, 吉野裕高

    日本物理学会2022年度秋季大会  2022.9.8 

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    Event date: 2022.9

    Language:Japanese  

  3. Area bound for surfaces in general relativity Invited International conference

    Keisuke Izumi

    LeCosPA 4th International Symposium Unity of Physics – From Plasma Wakefields to Black Holes  2021.12.3 

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    Event date: 2021.11 - 2021.12

    Language:English   Presentation type:Oral presentation (invited, special)  

    Venue:LeCosPA   Country:Taiwan, Province of China  

  4. Area bound for surfaces in general relativity International conference

    Keisuke Izumi

    Strings and Fields 2021  2021.8.23 

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    Event date: 2021.8

    Language:English   Presentation type:Oral presentation (general)  

  5. Area bound for surfaces in generic gravitational field International conference

    K. Izumi

    Online JGRG Webinar Series 

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    Event date: 2021.3

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  6. S行列ユニタリ性と繰り込み可能性

    阿部 裕悟、稲見 武夫、泉 圭介

    日本物理学会 第 76 回年次大会 

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    Event date: 2021.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  7. Causal structures in Gauss-Bonnet gravity Invited International conference

    Keisuke Izumi

    Miyazaki Workshop on Particle Physics and Cosmology in 2020  

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    Event date: 2020.1

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  8. Causal structures in Gauss-Bonnet gravity Invited International conference

    Keisuke Izumi

    4th Korea-Japan bilateral workshop on String axion cosmology 

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    Event date: 2020.1

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  9. Invertible field transformations with derivatives: necessary and sufficient conditions Invited International conference

    Keisuke Izumi

    Gravitation and Mathematical Relativity 

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    Event date: 2019.12

    Language:English   Presentation type:Oral presentation (general)  

    Country:China  

  10. Causal structures in Gauss-Bonnet gravity Invited International conference

    Keisuke Izumi

    the APCTP workshop of Gravity, Strings and QM Matter 

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    Event date: 2019.11

    Language:English   Presentation type:Oral presentation (general)  

    Country:Korea, Republic of  

  11. Invertible field transformations with derivatives: necessary and sufficient conditions Invited International conference

    Keisuke Izumi

    3rd Korea-Japan bilateral workshop on String axion cosmology 

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    Event date: 2019.10

    Language:English   Presentation type:Oral presentation (general)  

    Country:Korea, Republic of  

  12. Penrose inequality for photon surface Invited International conference

    Keisuke Izumi

    Mini-workshop "Black holes and neutron stars imagination and reality" 

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    Event date: 2019.9

    Language:English   Presentation type:Oral presentation (general)  

    Country:Viet Nam  

  13. S-matrix Unitarity and Renormalizability Invited International conference

    Keisuke Izumi

    1-day Workshop on Quantum Gravity 

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    Event date: 2019.7

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  14. Locality and Causality Invited International conference

    Keisuke Izumi

    The 2nd Korea-Japan bilateral workshop on String Axion Cosmology 

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    Event date: 2019.1

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  15. Loosely trapped surface Invited International conference

    Keisuke Izumi

    Korea-Japan bilateral workshop on String axion cosmology 

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    Event date: 2018.11

    Language:English   Presentation type:Oral presentation (general)  

    Country:Korea, Republic of  

  16. On uniqueness of static black hole in Einstein-conformal scalar International conference

    Keisuke Izumi

    Korea-Japan bilateral workshop on String axion cosmology 

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    Event date: 2018.11

    Language:English   Presentation type:Oral presentation (general)  

    Country:Korea, Republic of  

  17. S-matrix Unitarity and Renormalizability International conference

    Keisuke Izumi

    Essential next steps for gravity and cosmology 

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    Event date: 2018.6

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  18. Optical theorem and renormalizability International conference

    Keisuke Izumi

    Gravitational Dynamics and Black Holes 

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    Event date: 2017.9

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  19. 因果構造解析 Invited

    泉 圭介

    相対論宇宙論 東北研究会 2017  

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    Event date: 2017.8

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  20. トレースアノマリー効果を古典作用で表す際の境界項

    泉 圭介、 C.-M. Shen、 P. Chen

    日本物理学会 第 72 回年次大会 

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    Event date: 2017.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  21. Theoretical constraints on modified theories of gravity International conference

    Keisuke Izumi

    The 3rd KMI International Symposium on "Quest for the Origin of Particles and the Universe" 

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    Event date: 2017.1

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  22. Causal structures in Gauss-Bonnet gravity International conference

    K. Izumi

    General relativity in higher dimensions -recent progress and future perspective 

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    Event date: 2016.11

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  23. Tree-Unitarity and renormalizability in Lifshitz-scaling theory -- as a toy model of Horava's gravity theory International conference

    T. Fujimori, T. Inami, K. Izumi, T. Kitamura

    Everything about Gravity 

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    Event date: 2015.12

    Language:English   Presentation type:Oral presentation (general)  

    Country:Taiwan, Province of China  

  24. Renormalization and Unitarity in Lifshitz-scaling theory International conference

    Keisuke Izumi

    the 2nd mini-workshop on gravity and cosmology 

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    Event date: 2015.10

    Language:English   Presentation type:Oral presentation (general)  

    Country:France  

  25. Causal structures in Massive gravity and Gauss-Bonnet gravity Invited International conference

    S.Deser, K. Izumi, Y. C. Ong, A. Waldron

    Superluminality in Effective Field Theories for Cosmology 

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    Event date: 2015.4

    Language:English   Presentation type:Oral presentation (general)  

    Country:Canada  

  26. Causality in modified gravity theory International conference

    S.Deser, K. Izumi, Y. C. Ong, A. Waldron

    19th International Symposium on Particles, Strings and Cosmology 

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    Event date: 2013.11

    Language:English   Presentation type:Oral presentation (general)  

    Country:Taiwan, Province of China  

  27. Is there acausality in Massive Gravity? International conference

    K. Izumi, Y. C. Ong

    Massive gravity and its cosmological implications 

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    Event date: 2013.4

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  28. Cosmological Perturbation in f(T) gravity Revisited and Importance of Nonlinearity International conference

    K. Izumi, Y. C. Ong

    The 4th APCosPA Winter School/Workshop on Cosmology and Particle 

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    Event date: 2013.1 - 2013.2

    Language:English   Presentation type:Oral presentation (general)  

    Country:Taiwan, Province of China  

  29. Trispectrum estimation in various models of equilateral type non-Gaussianity International conference

    K. Izumi, S. Mizuno, K. Koyama 

    2012 Asia Pacific School/Workshop on Cosmology and Gravitation 

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    Event date: 2012.3

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  30. Nonlinear analysis in Hořava gravity International conference

    Gravity, Lorentz Violation & Superluminality 

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    Event date: 2011.7

    Language:English   Presentation type:Oral presentation (general)  

    Country:Russian Federation  

  31. Non-Gaussianity from Horava-Lifshitz Cosmology

    泉 圭介、小林 洸、向山 信治

    日本物理学会2010年秋季大会 

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    Event date: 2010.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  32. Trispectrum in ghost inflation International conference

    K. Izumi, S. Mukohyama

    The non-Gaussian universe 

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    Event date: 2010.3

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  33. Stellar center is dynamical in Horava-Lifshitz gravity

    泉 圭介、向山 信治

    日本物理学会第65回年次大会 

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    Event date: 2010.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  34. 厳密解の系統的構成

    泉 圭介

    基研研究会 高次元Black Hole研究最前線 

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    Event date: 2009.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  35. No static star solution in Horava Gravity International conference

    K. Izumi, S. Mukohyama

    The 19th Workshop on General Relativity and Gravitation in Japan 

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    Event date: 2009.11 - 2009.12

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  36. de Sitter時空中のスピン2ゴースト

    泉 圭介、 田中 貴浩

    日本物理学会第64回年次大会 

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    Event date: 2009.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  37. About the ghost in DGP brane-world International conference

    The 18th Workshop on General Relativity and Gravitation in Japan 

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    Event date: 2008.11

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  38. Orthogonal black di-ring solution

    泉 圭介

    日本物理学会2008年春季大会 

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    Event date: 2008.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  39. Renormalized Newtonian Cosmic Evolution International conference

    The Theoretical Modeling of Cosmic Structure Formation and its Recent Progress 

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    Event date: 2008.3

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  40. Renormalized Newtonian Cosmic Evolution with Primordial Non-Gaussianity International conference

    K. Izumi and J. Soda

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    Event date: 2007.12

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

  41. Bubbles in DGP

    泉 圭介、小山 和哉、田中 貴浩、Oriol Pujolas

    日本物理学会第62回年次大会 

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    Event date: 2007.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  42. ABOUT THE GHOST IN THE MASSIVE GRAVITY THEORY International conference

    K. Izumi and T. Tanaka

    The 18th International Conference on General Relativity and Gravitation 

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    Event date: 2007.7

    Language:English   Presentation type:Oral presentation (general)  

    Country:Australia  

  43. DGPブレーンワールドのゴーストについて

    泉 圭介、小山 和哉、田中 貴浩

    日本物理学会2007年春季大会 

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    Event date: 2007.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  44. Unexorcized ghost in DGP brane world International conference

    K. Izumi, K. Koyama, T. Tanaka

    Brane-World Gravity 

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    Event date: 2006.9

    Language:English   Presentation type:Oral presentation (general)  

    Country:United Kingdom  

  45. DGPブレーンワールドにおけるゴースト粒子の評価

    泉 圭介、 田中 貴浩

    日本物理学会第61回年次大会 

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    Event date: 2006.3

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  46. Avoidance of ghost problem in DGP braneworld model International conference

    K. Izumi, T. Tanaka

    The Fifteenth Workshop on General Relativity and Gravitation in Japan 

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    Event date: 2005.11 - 2005.12

    Language:English   Presentation type:Oral presentation (general)  

    Country:Japan  

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KAKENHI (Grants-in-Aid for Scientific Research) 3

  1. Weak gravity conjectue and its application to particle physics and cosmology

    Grant number:20H01902  2020.4 - 2024.3

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

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    Authorship:Coinvestigator(s)  Grant type:Competitive

    Grant amount:\678000 ( Direct Cost: \600000 、 Indirect Cost:\78000 )

  2. The Einstein Equation and Three Dimensional Manifolds

    Grant number:17H01091  2017.4 - 2022.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (A)

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    Authorship:Coinvestigator(s)  Grant type:Competitive

    Grant amount:\1690000 ( Direct Cost: \1300000 、 Indirect Cost:\390000 )

  3. Analysis of the superluminal modes by gravitational quantum effect

    Grant number:17K14281  2017.4 - 2020.3

    Izumi Keisuke

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    Authorship:Principal investigator  Grant type:Competitive

    Grant amount:\4160000 ( Direct Cost: \3200000 、 Indirect Cost:\960000 )

    The purpose of this project is to understand the quantum gravity by investigating the classical causality and its quantum object unitarity.
    In the classical research, the concept of photon surface, that is defined only in static spacetimes, is extended to generic spacetimes. It has been shown that the area of the extended photon surface has an upper bound, and the hoop conjecture for it is established in some examples.
    In the quantum research, the conjecture between unitarity and renormalizability is investigated. Although theories with higher derivatives are its counter examples, we have introduced a new concept S-matrix unitarity, and posited a new conjecture between S-matrix unitarity and renormalizability. We have seen our conjecture is established even in theories with higher derivatives.

 

Teaching Experience (On-campus) 7

  1. Exercise in Mathematics I

    2020

  2. 数学演習Ⅰ

    2019

  3. 数学演習II

    2018

  4. 数学演習V

    2017

  5. 数学演習VI

    2017

  6. 数学演習V

    2016

  7. 数学演習VI

    2016

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Social Contribution 7

  1. 時空の幾何学

    Role(s):Appearance, Lecturer

    愛知県立豊田西高等学校  豊西総合大学  2021.11

  2. 都城高専 物理特別講演会 (外部講師講話)

    Role(s):Lecturer

    2019.1

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    Audience: High school students

  3. NHK カルチャー 名古屋教室 「数学散策」

    Role(s):Lecturer

    2018.2

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    Audience: General

  4. 2017 年度名古屋大学数学公開講座

    Role(s):Lecturer

    2017.10

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    Audience: High school students

  5. 平成 29 年度名古屋大学数学アゴラ

    Role(s):Lecturer

    2017.8

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    Audience: High school students

  6. 第58回名大祭 研究公開セミナー

    Role(s):Lecturer

    2017.6

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    Audience: High school students, College students, General

  7. NHK カルチャー 名古屋教室 「数学散策」

    Role(s):Lecturer

    2017.5

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    Audience: General

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