研究者詳細 - 泉　圭介

論文 - 泉　圭介

分割表示 89 件中 41 - 60 件目／全件表示 >>

Extension of photon surfaces and their area: Static and stationary spacetimes 査読有り国際誌 Open Access

Yoshino, H; Izumi, K; Shiromizu, T; Tomikawa, Y

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS 2017 巻 ( 6 ) 2017年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress of Theoretical and Experimental Physics

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 A0 of a TTS is proved to be bounded as A0 ≤ 4π(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 [Prog. Theor. Exp. Phys. 2017, 033E01 (2017)] is also examined.

DOI： 10.1093/ptep/ptx072

その他リンク： http://arxiv.org/pdf/1704.04637v2

On the uniqueness of the static black hole with conformal scalar hair 査読有り国際誌 Open Access

Tomikawa, Y; Shiromizu, T; Izumi, K

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS 2017 巻 ( 3 ) 2017年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress of Theoretical and Experimental Physics

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

DOI： 10.1093/ptep/ptx033

その他リンク： http://arxiv.org/pdf/1612.01228v3

Area bound for a surface in a strong gravity region 査読有り国際誌 Open Access

Shiromizu, T; Tomikawa, Y; Izumi, K; Yoshino, H

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS 2017 巻 ( 3 ) 2017年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress of Theoretical and Experimental Physics

For asymptotically flat spacetimes, using the inverse mean curvature flow we show that any compact 2-surface, S0, whose mean curvature and its derivative for the outward direction are positive in a spacelike hypersurface with non-negative Ricci scalar satisfies the inequality A0 ≤4π(3Gm)2, where A0 is the area of S0 and m is the total mass. The upper bound is realized when S0 is the photon sphere in a hypersurface isometric to a t = const. slice of the Schwarzschild spacetime.

DOI： 10.1093/ptep/ptx022

その他リンク： http://arxiv.org/pdf/1701.00564v2

Theoretical constraints on modified theories of gravity Open Access

Izumi K.

Proceedings of Science 2017-January 巻 2017年

出版者・発行元：Proceedings of Science

We discuss about the theoretical constraints on modified theories of gravity. To explain the dark component of the Universe, many modified theories of gravity have been proposed. Meanwhile, to quantize the gravitational theory, we would need a new theory of gravity in UV physics. In this talk, we focus on three theoretical aspects of gravitational theories; causal structures, positivity of energy and black hole physics. The recent developments of these topics were discussed.

DOI： 10.22323/1.294.0030

Hydro-elastic complementarity in black branes at large <i>D</i> 査読有り国際誌 Open Access

Emparan, R; Izumi, K; Luna, R; Suzuki, R; Tanabe, K

JOURNAL OF HIGH ENERGY PHYSICS 2016 巻 ( 6 ) 2016年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of High Energy Physics

Abstract: 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

その他リンク： http://arxiv.org/pdf/1602.05752v3

Tree-Unitarity and renormalizability in Lifshitz-scaling theory -- as a toy model of Hořava's gravity theory 査読有り

Toshiaki Fujimori, Takeo Inami, Keisuke Izumi, Tomotaka Kitamura

2016年1月

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

DOI： 10.1142/9789813203952_0054

その他リンク： http://arxiv.org/pdf/1601.06470v1

Tree-level unitarity and renormalizability in Lifshitz scalar theory 査読有り国際誌 Open Access

Fujimori, T; Inami, T; Izumi, K; Kitamura, T

PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS 2016 巻 ( 1 ) 2016年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress of Theoretical and Experimental Physics

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

その他リンク： http://arxiv.org/pdf/1510.07237v1

Boundary effect of anomaly-induced action (vol 92, 024035, 2015) 査読有り Open Access

Shen, CM; Izumi, K; Chen, PS

PHYSICAL REVIEW D 92 巻 ( 4 ) 2015年8月

Boundary effect of anomaly-induced action 査読有り

Che-Min Shen, Keisuke Izumi, Pisin Chen

PHYSICAL REVIEW D 92 巻 ( 2 ) 2015年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

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

Power-counting and renormalizability in Lifshitz scalar theory 査読有り国際誌 Open Access

Fujimori, T; Inami, T; Izumi, K; Kitamura, T

PHYSICAL REVIEW D 91 巻 ( 12 ) 2015年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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 counterterms 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 counterterms to appear. The symmetry requirements might have important implications for the construction of matter field sectors in the Hořava-Lifshitz gravity.

DOI： 10.1103/PhysRevD.91.125007

その他リンク： http://arxiv.org/pdf/1502.01820v1

Ghosts in the self-accelerating DGP branch with Gauss-Bonnet effect 査読有り国際誌 Open Access

Liu, YW; Izumi, K; Bouhmadi-López, M; Chen, PS

EUROPEAN PHYSICAL JOURNAL C 75 巻 ( 6 ) 2015年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：European Physical Journal C

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

その他リンク： http://arxiv.org/pdf/1405.0850v2

New definition of a wormhole throat 査読有り国際誌 Open Access

Tomikawa, Y; Izumi, K; Shiromizu, T

PHYSICAL REVIEW D 91 巻 ( 10 ) 2015年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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

The boundary effect of anomaly-induced action 査読有り

Che-Min Shen, Keisuke Izumi, Pisin Chen

Physical Review D 2015年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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

その他リンク： http://arxiv.org/pdf/1505.00959v1

Remnant symmetry, propagation, and evolution in <i>f</i>(<i>T</i>) gravity 査読有り国際誌 Open Access

Chen, PS; Izumi, K; Nester, JM; Ong, YC

PHYSICAL REVIEW D 91 巻 ( 6 ) 2015年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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 nonunique 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

その他リンク： http://arxiv.org/pdf/1412.8383v3

Problems of massive gravities 査読有り国際誌 Open Access

Deser, S; Izumi, K; Ong, YC; Waldron, A

MODERN PHYSICS LETTERS A 30 巻 ( 3-4 ) 2015年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Modern Physics Letters A

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

Boundary effect of anomaly-induced action 査読有り国際誌

Che-Min Shen, Keisuke Izumi, Pisin Chen

Physical Review D 2015年

Wormhole on DGP brane 査読有り国際誌 Open Access

Tomikawa, Y; Shiromizu, T; Izumi, K

PHYSICAL REVIEW D 90 巻 ( 12 ) 2014年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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 1010cm or so.

DOI： 10.1103/PhysRevD.90.126001

その他リンク： http://arxiv.org/pdf/1409.6816v2

DGP braneworld with a bubble of nothing 査読有り国際誌

Izumi, K; Shiromizu, T

PHYSICAL REVIEW D 90 巻 ( 4 ) 2014年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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. © 2014 American Physical Society.

DOI： 10.1103/PhysRevD.90.046005

Causal structures in Gauss-Bonnet gravity 査読有り国際誌 Open Access

Izumi, K

PHYSICAL REVIEW D 90 巻 ( 4 ) 2014年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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, RABNANB≥0 for any null vector NA, 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. © 2014 American Physical Society.

DOI： 10.1103/PhysRevD.90.044037

その他リンク： http://arxiv.org/pdf/1406.0677v2

Acausality and nonunique evolution in generalized teleparallel gravity 査読有り国際誌 Open Access

Izumi, K; Gu, JA; Ong, YC

PHYSICAL REVIEW D 89 巻 ( 8 ) 2014年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

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. © 2014 American Physical Society.

DOI： 10.1103/PhysRevD.89.084025

その他リンク： http://arxiv.org/pdf/1309.6461v2

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