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

Large Angle CMB Anisotropy in an Open Universe in the One-Bubble inflationary Scenario
We consider an alternative scenario of inflation which can account for a spatially open universe. It is similar to the old inflation in which the bubble nucleation occurs in the sea of the false vacuum, but it differs from the old inflation in that the second slow rollover inflation occurs inside a nucleated bubble. Hence, our observable universe is entirely contained in one nucleated bubble. The significance of the scenario is that apart from a variance caused by model parameters, it gives us a definite prediction on the spectrum of the primordial density perturbations, and hence it is observationally testable. Here we investigate the spectrum of cosmic microwave background anisotropies on large angular scales. We find that the contribution from peculiar modes which never appear in the usual harmonic analysis is significant in the case Ω0 ≲ 0.1.

DOI： 10.1086/176588

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevD.110.085018

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

Understanding the phenomenon of quantum superposition of gravitational fields induced by massive quantum particles is an important starting point for quantum gravity. The purpose of this study is to deepen our understanding of the phenomenon of quantum superposition of gravitational fields. To this end, we consider a trade-off relation of entanglement (monogamy relation) in a tripartite system consisting of two massive particles and a gravitational field that may be entangled with each other. Consequently, if two particles cannot exchange information mutually, they are in a separable state, and the particle and gravitational field are always entangled. Furthermore, even when two particles can send information to each other, there is a trade-off between the two particles and the gravitational field. We also investigate the behavior of the quantum superposition of the gravitational field using quantum discord. We find that quantum discord increases depending on the length scale of the particle superposition. Our results may help understand the relationship between the quantization of the gravitational field and the meaning of the quantum superposition of the gravitational field.

DOI： 10.1103/PhysRevD.110.045016

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.110.045016/fulltext

Publisher：Physical Review A  

We investigate violations of Leggett-Garg inequalities (LGIs) for a harmonic oscillator and a (1+1)-dimensional chiral scalar field with coherent-state projectors, which is equivalent to a heterodyne-type measurement scheme. For the harmonic oscillator, we found that the vacuum and thermal states violated the LGIs by evaluating the two-time quasiprobability distribution function. In particular, we demonstrate that the value of the two-time quasiprobability reaches -0.123 for a squeezed coherent-state projector, which is equivalent to 98% of the Lüders bound corresponding to the maximal violation of the LGIs. We also find a violation of the LGIs for the local mode of a quantum chiral scalar field by constructing a coherent-state projector similar to the harmonic-oscillator case. In contrast with the harmonic oscillator, the periodicity in the time direction of the quasiprobability disappears, which is related to the existence of quantum entanglement between the local mode and its complementary degrees of freedom.

DOI： 10.1103/PhysRevA.110.022217

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We report the feasibility of detecting the gravity-induced entanglement (GIE) with optomechanical systems, which is the first investigation that clarifies the feasible experimental parameters to achieve a signal-to-noise ratio of S/N=1. Our proposal focuses on GIE generation between optomechanical mirrors, coupled via gravitational interactions, under continuous measurement, feedback control, and Kalman filtering process, which matured in connection with the field of gravitational wave observations. We solved the Riccati equation to evaluate the time evolution of the conditional covariance matrix for optomechanical mirrors that estimated the minimum variance of the motions. The results demonstrate that GIE is generated faster than a well-known time scale without optomechanical coupling. The fast generation of entanglement is associated with quantum-state squeezing by the Kalman filtering process, which is an advantage of using optomechanical systems to experimentally detect GIE.

DOI： 10.1103/PhysRevD.110.024057

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Language：Japanese   Publisher：The Physical Society of Japan  

<p>What is the gravity of a quantum system and what does it cause? This is a fundamental problem for unifying quantum mechanics and general relativity, which has not been elucidated yet. A key feature for elucidating the problem is the quantum superposition of a gravitational field, which may appear in the superposition of a quantum system with a mass. Interestingly, this quantum phenomenon of gravity generates entanglement in quantum systems. This gravity-induced entanglement can be a main target in the above context. In this article, we share the current studies on the gravity of a quantum system and on gravity-induced entanglement.</p>

DOI： 10.11316/butsuri.79.5_224

CiNii Research

Authorship：Last author  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

We investigate the quantum signature of gravity in optomechanical systems under quantum control. We analyze the gravity-induced entanglement and squeezing in mechanical mirrors in a steady state. The behaviors and the conditions for generating the gravity-induced entanglement and squeezing are identified in the Fourier modes of the mechanical mirrors. The condition of generating the entanglement between the mirrors found in the present paper is more severe than that of the gravity-induced entanglement between output lights. The gravity-induced entanglement in optomechanical systems is an important milestone toward verifying the quantum nature of gravity, which should be verified in the future.

DOI： 10.1103/PhysRevD.109.064090

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DOI： 10.1103/PhysRevA.109.032213

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

We evaluated the accuracy limit for estimating gravitational potential using optical lattice clocks by utilizing the quantum Cramér-Rao bound. We then compared the results for single-layer and multilayer optical lattice clocks. The results indicate that the lower bound of variance of the estimator of gravitational potential using finite-size optical lattice clocks diverges and recovers repeatedly as a function of time. Namely, the accuracy of the gravitational potential estimation is not a monotonic function of time owing to the effect of gravitational dephasing in finite-size optical lattice clocks. Further, this effect creates an estimation accuracy limit when attempting to avoid the divergence of the lower bound. When the number of layers in the optical lattice clock is sufficiently large, the limit is independent of the optical lattice clock details. The time required to reach this limit is calculated to be approximately 33 h for a three-dimensional optical lattice clock consisting of one million cadmium atoms due to Earth's gravity, and approximately the same for other atoms. This time is much longer than the current coherence time of 26s.

DOI： 10.1103/PhysRevA.108.063112

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

Investigating the quantum nature of gravity is an important issue in modern physics. Recently, studies pertaining to the quantum superposition of gravitational potential have garnered significant interest. Inspired by Mari et al. [Sci. Rep. 6, 22777 (2016)SRCEC32045-232210.1038/srep22777] and Baym and Ozawa [Proc. Natl. Acad. Sci. U.S.A. 106, 3035 (2009)PNASA60027-842410.1073/pnas.0813239106], Belenchia et al. [Phys. Rev. D 98, 126009 (2018)PRVDAQ2470-001010.1103/PhysRevD.98.126009] considered a gedanken experiment involving such a quantum superposition and mentioned that the superposition renders causality and complementarity inconsistent. They resolved this inconsistency by considering the quantized dynamical degrees of freedom of gravity. This suggests a strong relationship between the quantum superposition of the gravitational potential and the quantization of the gravitational field. In our previous study [Phys. Rev. D 106, 125002 (2022)PRVDAQ2470-001010.1103/PhysRevD.106.125002], we have shown that the quantum uncertainty of a field guarantees the consistency between causality and complementarity. In this study, we focus on the entanglement between two particles' states due to the electromagnetic/gravitational potential and investigate its relationship with quantum uncertainty, causality, and complementarity. Our numerical analyses show that the quantum uncertainty of the electromagnetic/gravitational field results in vacuum fluctuations and prohibits the entanglement between two particles' states when causality is satisfied. We further demonstrate that complementarity holds when the particles do not get entangled. The uncertainty relation does not cause the entanglement between two particles' states, which guarantees complementarity.

DOI： 10.1103/PhysRevD.108.105019

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Physical Review A  

Pendulums have long been used as force sensors due to their ultimately low dissipation (high-quality factor) characteristic. They are widely used in the measurement of the gravitational constant, detection of gravitational waves, and determination of ultralight dark matter. Furthermore, it is expected that the quantum nature of gravity will be demonstrated by performing quantum control for macroscopic pendulums. Recently, we have demonstrated that quantum entanglement between two pendulums can be generated using an optical spring [D. Miki, N. Matsumoto, A. Matsumura, T. Shichijo, Y. Sugiyama, K. Yamamoto, and N. Yamamoto, Phys. Rev. A 107, 032410 (2023)10.1103/PhysRevA.107.032410]; however, we have ignored that an optical spring can reduce the quality factor (Q factor) by applying normal-mode splitting between the pendulum and rotational modes possessing relatively high dissipation. Herein, we analyze a system composed of a cylinder suspended using a beam (a suspended mirror, i.e., a pendulum) and an optical spring to consider normal-mode splitting. The reduction in Q factor is determined only by the beam parameters: the ratio of the radius of the mirror to the length of the beam, and the ratio of the frequency of the rotational mode to the pendulum mode in the absence of cavity photons. In our analysis, we find that the reduction factor 4.38 is reproduced, which is consistent with the experimental result in Matsumoto et al. [N. Matsumoto, S. B. Cataño-Lopez, M. Sugawara, S. Suzuki, N. Abe, K. Komori, Y. Michimura, Y. Aso, and K. Edamatsu, Phys. Rev. Lett. 122, 071101 (2019)0031-900710.1103/PhysRevLett.122.071101]. Our analysis shows that low dissipation (high quality) can be reached using an optical spring for the realistic pendulum system considering the rotational degree of freedom.

DOI： 10.1103/PhysRevA.107.033515

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Physical Review A  

This paper is aimed at investigating the feasibility of generating quantum conditional entanglement between macroscopic mechanical mirrors in optomechanical systems while under continuous measurement and feedback control. We consider the squeezing of the states of the mechanical common and the differential motions of the mirrors by the action of measuring the common and the differential output light beams in the Fabry-Pérot-Michelson interferometer. We carefully derive a covariance matrix for the mechanical mirrors in a steady state, employing the Kalman filtering problem with dissipative cavities. We demonstrate that Gaussian entanglement between the mechanical mirrors is generated when the states of the mechanical common and differential modes of the mirrors are squeezed with high purity in an asymmetric manner. Our results also show that quantum entanglement between 7-mg mirrors is achievable in the short term.

DOI： 10.1103/PhysRevA.107.032410

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Progress of Theoretical and Experimental Physics  

We study the system of a massive fermion field confined between two parallel plates, where the properties of both plates are discussed under chiral MIT boundary conditions. We investigate the effects of the chiral angle on the Casimir energy for a massive fermion field with the general momentum. We find that the Casimir energy as a function of the chiral angle is generally symmetric, and the attractive Casimir force in the chiral case is stronger than that in the nonchiral case. In addition, we investigate the approximate Casimir energy for light and heavy mass cases. The behavior of the discrete momentum and changes of spin orientation are also discussed.

DOI： 10.1093/ptep/ptac172

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

It has long been debated whether gravity should be quantized or not. Recently, the authors in [Sci. Rep. 6, 22777 (2016)SRCEC32045-232210.1038/srep22777; Proc. Natl. Acad. Sci. U.S.A. 106, 3035 (2009)PNASA60027-842410.1073/pnas.0813239106] discussed the inconsistency between causality and complementarity in a Gedankenexperiment involving the quantum superposition of massive/charged bodies, and Belenchia et al. [Phys. Rev. D 98, 126009 (2018)PRVDAQ2470-001010.1103/PhysRevD.98.126009; Int. J. Mod. Phys. D 28, 1943001 (2019)IMPDEO0218-271810.1142/S0218271819430016] resolved the inconsistency by requiring the quantum radiation and vacuum fluctuations of gravitational/electromagnetic field. Stimulated by their works, we reanalyze the consistency between the two physical properties, causality and complementarity, according to the quantum field theory. In this analysis, we consider a Gedankenexperiment inspired by [Sci. Rep. 6, 22777 (2016)SRCEC32045-232210.1038/srep22777; Proc. Natl. Acad. Sci. U.S.A. 106, 3035 (2009)PNASA60027-842410.1073/pnas.0813239106; Phys. Rev. D 98, 126009 (2018)PRVDAQ2470-001010.1103/PhysRevD.98.126009; Int. J. Mod. Phys. D 28, 1943001 (2019)IMPDEO0218-271810.1142/S0218271819430016], in which two charged particles coupled with a photon field are in a superposition of two trajectories. First, we observe that causality is satisfied by the retarded propagation of the photon field. Next, by introducing an inequality between visibility and which-path information, we show that the quantum radiation and vacuum fluctuations of the photon field ensure complementarity. We further find that the Robertson inequality associated with the photon field leads to the consistency between causality and complementarity in our Gedankenexperiment. Finally, we mention that a similar feature appears in the quantum field of gravity.

DOI： 10.1103/PhysRevD.106.125002

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The Bose-Marletto-Vedral experiment is a proposal for testing the quantum nature of gravity with entanglement due to Newtonian gravity. This proposal has stimulated controversy on how the entanglement due to Newtonian gravity is related to the essence of quantum gravity and the existence of gravitons. Motivated by this, we analyze the entanglement generation between two charged particles coupled to a photon field. We assume that each particle is in a superposition of two trajectories and that the photon field is initially in a coherent state. Based on covariant quantum electrodynamics, the formula for the entanglement negativity of the charged particles is derived for the first time. Adopting simple analytic trajectories of the particles, we demonstrate the entanglement between them. It is observed that the entanglement is suppressed by the decoherence due to the vacuum fluctuations of the photon field. We also find that the effect of quantum superposition of bremsstrahlung appears in the entanglement negativity formula. The similar structures between the gravity theory and electromagnetic theory suggests that a similar feature may be observed in the entanglement generation by quantum gravitational radiation.

DOI： 10.1103/PhysRevD.106.045009

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

Expanding edge experiments are promising to open new physics windows of quantum Hall systems. In a static edge, the edge excitation, which is described by free fields decoupled with the bulk dynamics, is gapless, and the dynamics preserve conformal symmetry. When the edge expands, such properties need not be preserved. We formulate a quantum field theory in 1 ?? 1-dimensional curved spacetimes to analyze the edge dynamics. We propose methods to address the following questions using edge waveforms from the expanding region: Does the conformal symmetry survive? Is the nonlinear interaction of the edge excitations induced by edge expansion? Do the edge excitations interact with the bulk excitations? We additionally show that the expanding edges can be regarded as expanding universe simulators of twodimensional dilaton-gravity models, including the Jackiw-Teitelboim gravity model. As an application, we point out that our theoretical setup might simulate emission of analog Hawking radiation with the GibbonsHawking temperature from the future de Sitter horizon formed in the expanding-edge region.

DOI： 10.1103/PhysRevD.105.105009

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The standard cosmological model assumes a homogeneous and isotropic universe as the background spacetime on large scales called the cosmological principle. However, some observations suggest the possibility of an inhomogeneous and anisotropic universe at large scales. In this paper, we investigate a model of the Universe with random inhomogeneities and anisotropies on very large scales, motivated by the supercurvature dark energy model in Nan et al. [Phys. Rev. D 99, 103512 (2019)PRVDAQ2470-001010.1103/PhysRevD.99.103512]. In this model, the authors introduced a scalar field with O(1) inhomogeneities on a scale sufficiently larger than the current horizon scale (superhorizon scale), and the potential energy of the scalar field explains the accelerating expansion, with slight deviations from the cosmological principle. We aim at clarifying the theoretical prediction on the large-scale structure (LSS) of the matter component in this model. Based on the work on the superhorizon scale fluctuations (superhorizon mode) presented in Y. Nan and K. Yamamoto [Phys. Rev. D 105, 063518 (2022)PRVDAQ2470-001010.1103/PhysRevD.105.063518], we derive the equations that the perturbative components to the LSS obey as a generalization of the cosmological perturbations theory, which is solved to find the influence of the dark energy inhomogeneities on the formation of the LSS. Finally, we show that the model can be consistent with observations by comparing the σ8 predicted by the numerical solution of the model with the σ8 indicated by observations such as Planck and the Sloan Digital Sky Survey.

DOI： 10.1103/PhysRevD.105.083531

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society ({APS})  

We consider a dynamical model for dark energy based on an ultralight mass scalar field with very large-scale inhomogeneities. This model may cause observable impacts on the anisotropic properties of the cosmic microwave background (CMB) intensity and luminosity distance. We formulate the model as the cosmological perturbations of the superhorizon scales, focusing on the local region of our universe. Moreover, we investigated the characteristic properties of the late-time evolution of inhomogeneous dark energy. Our numerical solutions show that the model can mimic the standard ΛCDM cosmology while including spatially dependent dark energy with flexible ranges of the model parameters. We put a constraint on the amplitude of these inhomogeneities of the dark energy on very large scales with the observations of the CMB anisotropies. We also discuss their influence on the estimation of the luminosity distance.

DOI： 10.1103/PhysRevD.105.063518

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Physical Review D  

We develop an entanglement criterion with third- and fourth-order cumulants to detect the entanglement of non-Gaussian states. The efficiency of the entanglement criterion is investigated for gravitating mirrors in optomechanical systems. We show that the entangled regime of the mirrors is enlarged by the third- and fourth-order cumulants. We also discuss the limitations of the entanglement criterion for mirrors in a highly non-Gaussian state.

DOI： 10.1103/PhysRevD.105.026011

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We investigate the effects of the chiral MIT boundary conditions for a Dirac particle in a 1D box. We show how the boundary condition affects the discrete momentum, energy level, transition frequency, and spin state in a box. The effects of the chiral MIT boundary conditions on the probability and scalar densities are also demonstrated. The results show that an asymmetric distribution appears in the box depending on the parameters of the spin orientation and chiral angle.

DOI： 10.1093/ptep/ptab122

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In this paper, we study the relativistic effect on the wave functions for a bouncing particle in a gravitational field. Motivated by the equivalence principle, we investigate the Klein-Gordon and Dirac equations in Rindler coordinates with the boundary conditions mimicking a uniformly accelerated mirror in Minkowski space. In the nonrelativistic limit, all these models in the comoving frame reduce to the familiar eigenvalue problem for the Schrödinger equation with a fixed floor in a linear gravitational potential, as expected. We find that the transition frequency between two energy levels of a bouncing Dirac particle is greater than the counterpart of a Klein-Gordon particle, while both are greater than their nonrelativistic limit. The different corrections to eigen-energies of particles of different nature are associated with the different behaviors of their wave functions around the mirror boundary.

DOI： 10.1142/S021827182150098X

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We study the thermal evolution of isolated neutron stars in scalar-tensor theories for the first time. Whether rapid cooling due to the direct Urca process occurs or not is an interesting question from the viewpoint of the temperature observation of isolated neutron stars. Moreover, investigation of the cooling effect of nucleon superfluidity also has large uncertainties, though it is important in modern cooling theory. The cooling effect is typically influenced by the proton fraction and the central density. If a fifth force is mediated due to a modification of gravity, the relation between the central density and mass of neutron stars differs from that in general relativity, and the cooling curve is also naively expected to vary. We find that an unscreened fifth force near the surface of neutron stars changes the mass-central density relation, and the direct Urca process can be triggered even for neutron stars with smaller mass. We also present cooling curves including nucleon superfluidity under the scalar-tensor theory. These results show that it might be useful to test gravitational theories with cooling observations of neutron stars.

DOI： 10.1093/ptep/ptab099

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

We study the relations of the positive frequency mode functions of Dirac field in 4-dimensional Minkowski spacetime covered with Rindler and Kasner coordinates, and describe the explicit form of the Minkowski vacuum state with the quantum states in Kasner and Rindler regions, and analytically continue the solutions. As a result, we obtain the correspondence of the positive frequency mode functions in Kasner region and Rindler region in a unified manner which derives vacuum entanglement.

DOI： 10.1103/PhysRevD.103.125005

Other Link： https://link.aps.org/doi/10.1103/PhysRevD.103.125005

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

We derive the solutions of gravitational waves in the future (F) expanding and past (P) shrinking Kasner spacetimes, as well as in the left (L) and right (R) Rindler wedges in the Regge-Wheeler gauge. The solutions for all metric components are obtained in an analytic form in each region. We identify the master variables, which are equivalent to massless scalar fields, to describe the gravitational degrees of freedom for the odd-parity and even-parity modes under the transformation in the two-dimensional plane-symmetric space. Then, the master variables are quantized, and we develop the quantum field theory of the gravitational waves in the F, P, L, and R regions. We demonstrate that the mode functions of the quantized gravitational waves in the left and right Rindler wedges are obtained by an analytic continuation of the left-moving and right-moving wave modes in Kasner spacetime. On the basis of these analyses, we discuss the Unruh effect of the quantized gravitational waves for an observer in a uniformly accelerated motion in Minkowski spacetime in an explicit manner for the first time.

DOI： 10.1103/PhysRevD.103.026017

Other Link： https://journals.aps.org/prd/abstract/10.1103/PhysRevD.103.083503

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We investigate large-scale inhomogeneity of dark energy in the bubble nucleation scenario of the universe. In this scenario, the present universe was created by a bubble nucleation due to quantum tunneling from a metastable ancestor vacuum, followed by a primordial inflationary era. During the bubble nucleation, supercurvature modes of some kind of a scalar field are produced, and remain until present without decaying; thus they can play a role of the dark energy, if the mass of the scalar field is sufficiently light in the present universe. The supercurvature modes fluctuate at a very large spatial scale, much longer than the Hubble length in the present universe. Thus they create large-scale inhomogeneities of the dark energy, and generate large-scale anisotropies in the cosmic microwave background (CMB) fluctuations. This is a notable feature of this scenario, where quantum fluctuations of a scalar field are responsible for the dark energy. In this paper, we calculate imprints of the scenario on the CMB anisotropies through the integrated Sachs-Wolfe (ISW) effect, and give observational constraints on the curvature parameter ΩK and on an additional parameter ε describing some properties of the ancestor vacuum.

DOI： 10.1103/PhysRevD.99.103512

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

Late-time quantum radiation by a uniformly accelerated detector in de Sitter spacetime
We investigate the quantum radiation emitted by a uniformly accelerated Unruh-De Witt detector in de Sitter spacetime. We find that there exists a nonvanishing quantum radiation at late times in the radiation zone of the conformally flat coordinates, whic

DOI： 10.1103/PhysRevD.98.105012

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

Gravitational redshift in the void-galaxy cross-correlation function in redshift space
We construct an analytic model for the void-galaxy cross-correlation function that enables theoretical predictions of the dipole signal produced dominantly by the gravitational redshift within voids for the first time. By extending a theoretical formulation for the redshift-space distortion of galaxies to include the second order terms of the galaxy peculiar velocity v and the gravitational potential, we formulate the void-galaxy cross-correlation function multipoles in the redshift space, the monopole ξ0(s), dipole ξ1(s), and quadrupole ξ2(s). We find that the dipole ξ1(s) is dominated by the gravitational redshift, which provides a unique opportunity to detect the gravitational potential of voids. Thus, for the dipole ξ1(s)(s), the gravitational redshift is crucial. Although the higher order effect is almost negligible on the monopole ξ0(s), it has an influence on the quadrupole ξ2(s). The effects from the random velocity of galaxies and the definition of the void center on the dipole signal are also discussed. Our model offers a new theoretical probe for the detection of gravitational redshift with voids and further tests on cosmology and gravity.

DOI： 10.1103/PhysRevD.98.043527

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

Higher multipoles of the galaxy bispectrum in redshift space
As a generalization of our previous work [Phys. Rev. D 95 (2017) 043528], in which an analytic model for the galaxy bispectrum in redshift space was developed on the basis of the halo approach, we here investigate its higher multipoles that have not been known so far. The redshift-space bispectrum includes the two variables ω and φ for the line-of-sight direction, and the higher multipole bispectra are defined by the coefficients in the expansion of the redshift-space bispectrum using the spherical harmonics. We find 6 new nonvanishing components out of 25 total components up to ℓ=4, in addition to 3 components discussed in the previous work (monopole, quadruple, and hexadecapole of m=0). The characteristic behaviors of the new nonvanishing multipoles are compared with the results of galaxy mock catalogs that match the halo occupation distribution of the Sloan Digital Sky Survey Baryonic Oscillation Spectroscopic Survey low-redshift sample. We find that the multipoles with m≠ 0 are also sensitive to redshift-space distortion (RSD) as well as those with m=0 and thus are key ingredients in the RSD analysis using the galaxy bispectrum. Analytic approximation formulas for these nonzero components are also presented; these are useful for understanding the characteristic behaviors.

DOI： 10.1088/1475-7516/2018/07/038

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

We investigate gravitational redshifts (signals of gravitational potential) in measurements of the redshifts of cosmological objects, i.e., central and satellite galaxies in clusters of galaxies, intracluster gas, as well as galaxies associated with voids by developing simple theoretical models. In the analysis with satellite galaxies in clusters, we develop a very simple analytic model for satellite galaxies virialized in halos, which enables us to evaluate the signals depending on the properties of the halo occupation distribution of galaxies. We obtain results consistent with recent previous results, though our results are restricted to the satellite galaxies inside the virial radius. In the analysis of intracluster gas, we develop a simple analytic model including the effect of random motions of gases, which are assumed to generate nonthermal pressure. We demonstrate a possible contribution of the random motions of gases to gravitational potential measurements. We also investigate a possible signature of the gravitational potential in measurements of galaxies associated with voids by utilizing a simple analytic model. We show that the second-order Hubble term, which appears in the expansion of the scale factor around the center of a void, may make a significant contribution depending on the way the galaxy samples are analyzed. The studies on the possible signals of gravitational potential for intracluster gases and voids are performed for the first time.

DOI： 10.1103/PhysRevD.97.063512

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

The Minkowski vacuum state is expressed as an entangled state between the left and right Rindler wedges when it is constructed on the Rindler vacuum. In this paper, we further examine the entanglement structure and extend the expression to the future (expanding) and past (shrinking) Kasner spacetimes. This clarifies the origin of the quantum radiation produced by an Unruh-DeWitt detector in uniformly accelerated motion in the four-dimensional Minkowski spacetime. We also investigate the two-dimensional massless case where the quantum radiation vanishes but the same entanglement structure exists.

DOI： 10.1103/PhysRevD.96.083531

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

Path Integral Formulation for Wave Effect in Multilens System

DOI： 10.4236/ijaa.2017.73018

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

Quantum entanglement of the Minkowski vacuum state between left and right Rindler wedges generates thermal behavior in the right Rindler wedge, which is known as the Unruh effect. In this paper, we show that there is another consequence of this entanglement, namely entanglement-induced quantum radiation emanating from a uniformly accelerated object. We clarify why it is in agreement with our intuition that incoming and outgoing energy fluxes should cancel each other out in a thermalized state.

DOI： 10.1103/PhysRevD.96.045001

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

Unruh Radiation Produced by a Uniformly Accelerating Charged Particle in Thermal Random Motions

DOI： 10.1142/9789813203952_0082

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

We present an analytic formula for the galaxy bispectrum in redshift space on the basis of the halo approach description with the halo occupation distribution of central galaxies and satellite galaxies. This work is an extension of a previous work on the galaxy power spectrum, which illuminated the significant contribution of satellite galaxies to the higher multipole spectrum through the nonlinear redshift space distortions of their random motions. Behaviors of the multipoles of the bispectrum are compared with results of numerical simulations assuming a halo occupation distribution of the low-redshift (LOWZ) sample of the Sloan Digital Sky Survey (SDSS) III baryon oscillation spectroscopic survey (BOSS) survey. Also presented are analytic approximate formulas for the multipoles of the bispectrum, which is useful to understanding their characteristic properties. We demonstrate that the Fingers of God effect is quite important for the higher multipoles of the bispectrum in redshift space, depending on the halo occupation distribution parameters.

DOI： 10.1103/PhysRevD.95.043528

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We investigate the quantum radiation produced by an Unruh-DeWitt detector in a uniformly accelerating motion coupled to the vacuum fluctuations. Quantum radiation is nonvanishing, which is consistent with the previous calculation by Lin and Hu [Phys. Rev. D 73, 124018 (2006)]. We infer that this quantum radiation from the Unruh-De Witt detector is generated by the nonlocal correlation of the Minkowski vacuum state, which has its origin in the entanglement of the state between the left and the right Rindler wedges.

DOI： 10.1103/PhysRevD.95.023512

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

DOI： 10.1103/PhysRevD.94.064059

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

We investigate a constraint on reheating followed by alpha-attractor-type inflation (the E-model and T-model) from an observation of the spectral index n(s). When the energy density of the Universe is dominated by an energy component with the cosmic equation-of-state parameter w(re) during reheating, its e-folding number N-re and the reheating temperature T-re are bounded depending on w(re). When the reheating epoch consists of two phases-where the energy density of the Universe is dominated by uniform inflaton field oscillations in the first phase and by relativistic nonthermalized particles in the second phase-we find a constraint on the e-folding number of the first oscillation phase, N-sc, depending on the parameters of the inflaton potential. For the simplest perturbative reheating scenario, we find the lower bound for a coupling constant of inflaton decay in the E-model and T-model depending on the model parameters. We also find a constraint on the a parameter, alpha >= 0.01, for the T-model and E-model when we assume a broad resonance

DOI： 10.1103/PhysRevD.93.083524

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

We investigate the properties of quantum radiation produced by a uniformly accelerating charged particle undergoing thermal random motion, which originates from the coupling to the vacuum fluctuations of the electromagnetic field. Because the thermal random motion is regarded to result from the Unruh effect, the quantum radiation might give us hints of the Unruh effect. The energy flux of the quantum radiation is negative and smaller than that of Larmor radiation by one order in a/m, where a is the constant acceleration and m is the mass of the particle. Thus, the quantum radiation appears to be a suppression of the classical Larmor radiation. The quantum interference effect plays an important role in this unique signature. The results are consistent with the predictions of a model consisting of a particle coupled to a massless scalar field as well as those of the previous studies on the quantum effect on the Larmor radiation.

DOI： 10.1103/PhysRevD.93.085016

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

DOI： 10.1088/1475-7516/2016/03/030

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

Non-linear redshift-space distortion known as the Fingers-of-God (FoG) effect is a major systematic uncertainty in redshift-space distortion studies conducted to test gravity models. The FoG effect has been usually attributed to the random motion of galaxies inside their clusters. When the internal galaxy motion is not well virialized, however, the coherent infalling motion towards the cluster centre generates the FoG effect. Here, we derive an analytical model of the satellite velocity distribution due to the infall motion combined with the random motion. We show that the velocity distribution becomes far from Maxwellian when the infalling motion is dominant. We use simulated subhalo catalogues to find that the contribution of infall motion is important to massive subhaloes and that the velocity distribution has a top-hat like shape as expected from our analytic model. We also study the FoG effect due to infall motion on the redshift-space power spectrum. Using simulated mock samples of luminous red galaxies constructed from haloes and massive subhaloes in N-body simulations, we show that the redshift-space power spectra can differ from expectations when the infall motion is ignored.

DOI： 10.1093/mnrasl/slv153

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

We investigate the hypothetical process of gravitational Cherenkov radiation, which may occur in modified gravity theories. We obtain a useful constraint on a modified dispersion relation for propagating modes of gravitational waves, which could be predicted as a consequence of the violation of the Lorentz invariance in modified theories of gravity. The constraint from gravitational Cherenkov radiation and that from direct measurements of the gravitational waves emitted by a compact binary system are complementary to each other.

DOI： 10.1103/PhysRevD.92.104036

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

We study the third order solutions of the cosmological density perturbations in Horndeski's most general scalar-tensor theory under the condition that the Vainshtein mechanism is at work. In this work, we thoroughly investigate the independence property of the functions describing the nonlinear mode couplings, which is also useful for models within general relativity. Then, we find that the solutions of the density contrast and the velocity divergence up to third order are characterized by six parameters. Furthermore, the one-loop order power spectra obtained with third order solutions are described by four parameters. We exemplify the behavior of the one-loop order power spectra assuming the kinetic gravity braiding model, which demonstrates that the effect of modified gravity appears more significantly in the power spectrum of the velocity divergence than the density contrast.

DOI： 10.1103/PhysRevD.92.104033

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

We obtain a constraint on the parameters of a generalized cubic Galileon gravity model exhibiting the Vainshtein mechanism by using multi-wavelength observations of the Coma Cluster. The generalized cubic Galileon model is characterized by three parameters of the turning scale associated with the Vainshtein mechanism, and the amplitude of modifying a gravitational potential and a lensing potential. X-ray and Sunyaev-Zel'dovich (SZ) observations of the intra-cluster medium are sensitive to the gravitational potential, while the weak-lensing (WL) measurement is specified by the lensing potential. A joint fit of a complementary multi-wavelength dataset of X-ray, SZ and WL measurements enables us to simultaneously constrain these three parameters of the generalized cubic Galileon model for the first time. We also find a degeneracy between the cluster mass parameters and the gravitational modification parameters, which is influential in the limit of the weak screening of the fifth force.

DOI： 10.1088/1475-7516/2015/10/064

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

A particle in a uniformly accelerated motion exhibits Brownian random motions around the classical trajectory due to the coupling to the field vacuum fluctuations. Previous works show that the Brownian random motions satisfy the energy equipartition relation. This thermal property is understood as the consequence of the Unruh effect. In the present work, we investigate the radiation from the thermal random motions of an accelerated particle coupled to vacuum fluctuations. The energy flux of this radiation is negative of the order smaller than the classical radiation by the factor a/m, where a is the acceleration constant and m is the mass of a particle. The results could be understood as a suppression of the classical radiation by the quantum effect.

DOI： 10.1103/PhysRevD.92.045027

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

We investigate the potential of the higher multipole power spectra of the galaxy distribution in redshift space as a cosmological probe on halo scales. Based on the fact that a halo model explains well the multipole power spectra of the luminous red galaxy sample in the Sloan Digital Sky Survey, we focus our investigation on the random motions of the satellite luminous red galaxies that determine the higher multipole spectra at large wave numbers. We show that our theoretical model fits the higher multipole spectra at large wave numbers from N-body numerical simulations, and we apply these results for testing the gravity theory and the velocity structure of galaxies on the halo scales. In this analysis, we use the multipole spectra P-4(k) and P-6(k) on the small scales of the range of wave number 0.3 <= k/[hMpc(-1)] <= 0.6, which is in contrast to the usual method of testing gravity by targeting the linear growth rate on very large scales. We demonstrate that our method could be useful for testing gravity on the halo scales.

DOI： 10.1103/PhysRevD.92.023523

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

We investigate Brownian motions of a particle coupled to vacuum fluctuations of a quantum field. The Unruh effect predicts that an observer in an accelerated motion sees the Minkowski vacuum as thermally excited. This addresses the problem of whether or not a thermal property appears in a perturbative random motion of a particle in an accelerated motion due to the coupling. We revisit this problem by solving the equation of motion of a particle coupled to vacuum fluctuations including the radiation reaction force. We compute a Fourier integral for the variance of the random velocity in a rigorous manner. Similarly, we consider a particle coupled to vacuum fluctuations in de Sitter spacetime motivated by the argument that an observer in de Sitter spacetime sees the Bunch-Davies vacuum as a thermally excited state with the Gibbons-Hawking temperature. Our investigation clarifies the condition that the energy equipartition relation arises in the Brownian motions of a particle.

DOI： 10.1103/PhysRevD.89.124028

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

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

DOI： 10.1103/PhysRevD.89.103008

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

Bispectrum of cosmological density perturbations in the most general second-order scalar-tensor theory
We study the bispectrum of matter density perturbations induced by the large-scale structure formation in the most general second-order scalar-tensor theory that may possess the Vainshtein mechanism as a screening mechanism. On the basis of the standard perturbation theory, we derive the bispectrum being expressed by a kernel of the second-order density perturbations. We find that the leading-order kernel is characterized by one parameter, which is determined by the solutions of the linear density perturbations, the Hubble parameter, and the other function specifying nonlinear interactions. This is because our model, which may be equipped with the Vainshtein mechanism, includes only one simple function that describes mode couplings of the nonlinear interactions. This feature does not allow for varied behavior in the bispectrum of the matter density perturbations in the most general second-order scalar-tensor theory equipped with the Vainshtein mechanism. We exemplify the typical behavior of the bispectrum in a kinetic gravity braiding model. © 2014 American Physical Society.

DOI： 10.1103/PhysRevD.89.104007

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

We propose a novel method to test the gravitational interactions in the outskirts of galaxy clusters. When gravity is modified, this is typically accompanied by the introduction of an additional scalar degree of freedom, which mediates an attractive fifth force. The presence of an extra gravitational coupling, however, is tightly constrained by local rmasurements. In chameleon modifications of gravity, local tests can be evaded by employing a screening mechanism that suppresses the fifth force in dense environments. While the chameleon field may be screened in the interior of the cluster, its outer region can still be affected by the extra force, introducing a deviation between the hydrostatic and lensing mass of the cluster. Thus, the chameleon modification can be tested by combining the gas and lensing measurements of the cluster. We demonstrate the operability of our method with the Coma cluster, for which both a lensing measurement and gas observations from the X-ray surface brightness, the X-ray temperature, and the Sunyaev-Zer'dovich effect are available. U sing the,joint observational data set, we perform a Markov chain Monte Carlo analysis of the parameter space describing the different profiles in both the Newtonian and chameleon scenarios. We report competitive constraints on the chameleon field amplitude and its coupling strength to matter. In the case of f ( R) gravity, corresponding to a specific choice of the coupling, we find an upper bound on the background field amplitude of vertical bar fRo vertical bar < 6 x 10(-5), which is currently the tightest constraint on cosmological scales.

DOI： 10.1088/1475-014/04/013

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

Simultaneous constraints on the growth of structure and cosmic expansion from the multipole power spectra of the SDSS DR7 LRG sample
The anisotropic galaxy clustering on large scales provides us with a unique opportunity to probe into the gravity theory through the redshift-space distortions (RSDs) and theAlcock-Paczynski effect. Using the multipole power spectra up to hexadecapole (ℓ = 4), of the luminous red galaxy (LRG) sample in the Data Release 7 (DR7) of the Sloan Digital Sky Survey II (SDSS-II), we obtain simultaneous constraints on the linear growth rate f, angular diameter distance DA, and Hubble parameter H at redshift z = 0.3. For this purpose, we first extensively examine the validity of a theoretical model for the non-linear RSDs using mock subhalo catalogues from N-body simulations, which are constructed to match with the observed multipole power spectra. We show that the input cosmological parameters of the simulations can be recovered well within the error bars by comparing the multipole power spectra of our theoretical model and those of the mock subhalo catalogues. We also carefully examine systematic uncertainties in our analysis by testing the dependence on prior assumption of the theoretical model and the range ofwavenumbers to be used in the fitting. These investigations validate that the theoretical model can be safely applied to the real data. Thus, our results from the SDSS DR7 LRG sample are robust including systematics of theoretical modelling; f(z = 0.3)7sigma; 8(z = 0.3) = 0.49 ± stat.0.08 ± sys.0.04, DA(z = 0.3) = 968 ± stat.42 ± sys.17 (Mpc), H(z = 0.3) = 81.7 ± stat.5.0 ± sys.3.7 (km s-1 Mpc-1). We believe that our method to constrain the cosmological parameters using subhaloes catalogues will be useful for more refined samples like CMASS and LOWZ catalogues in the Baryon Oscillation Spectroscopic Survey in SDSS-III. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

DOI： 10.1093/mnras/stu111

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

We study the impacts of the satellite galaxies on the redshift-space distortions. In our multipole power spectrum analysis of the luminous red galaxies (LRGs) samples of the Sloan digital sky survey (SDSS), we have clearly detected the non-zero signature of the hexadecapole and tetrahexadecapole spectrum, which almost disappears in the power spectrum with the sample of the brightest LRGs only. We thus demonstrate that the satellite LRGs in multiple systems make a significant contribution to the multipole power spectrum though its fraction is small. The behavior can be understood by a simple halo model, in which the one-halo term, describing the Finger of God (FoG) effect from the satellite galaxies, makes the dominant contribution to the higher multipole spectra. We demonstrate that the small-scale information of higher multipole spectrum is useful for calibrating the satellite FoG effect and improves the measurement of the cosmic growth rate dramatically. We further demonstrate that the fiber collision in the galaxy survey influences the one-halo term and the higher multipole spectra, because the number of satellite galaxies in the halo occupation distribution (HOD) is changed. We also discuss about the impact of satellite galaxies on future high-redshift surveys targeting the H-alpha emitters.

DOI： 10.1088/1475-7516/2013/08/019

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

A uniformly accelerated detector (Unruh detector) in a Minkowski vacuum is excited as if it is exposed to a thermal bath with a temperature proportional to its acceleration. In the inertial frame, since both the excitation and de-excitation of the detector are accompanied by emission of radiation into the Minkowski vacuum, one may suspect that the Unruh detector emits radiation like Larmor radiation from an accelerated charged particle. However, it is known that the radiation is miraculously canceled out by a quantum interference effect. In this paper, we investigate the conditions under which the radiation cancels out. We first show that the cancellation occurs if the Green function satisfies a relation similar to the Kubo-Martin-Schwinger (KMS) condition. We then study two examples, Unruh detectors in 3+1-dimensional Minkowski spacetime and in de Sitter spacetime. In both cases, the relation holds only in a restricted region of the spacetime, but the radiation is canceled over the whole spacetime. Hence the KMS-like relation is necessary but not sufficient for the cancellation to occur.

DOI： 10.1093/ptep/ptt040

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

DOI： 10.4236/ijaa.2013.33029

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

We investigate the gas density, temperature, and pressure profiles in a dark matter halo under the influence of the chameleon force. We solve the hydrostatic equilibrium equation for the gas coupled with the chameleon field in an analytic manner, using an approximate solution for the chameleon field equation with the source term, with a generalized Navarro-Frenk-White universal density profile. We find that the gas distribution becomes compact because a larger pressure gradient is necessary due to the additional chameleon force. By confronting the theoretical prediction with the data of the temperature profile of the Hydra A cluster according to Suzaku x-ray observations out to the virial radius, we demonstrate that a useful constraint on a model parameter can be obtained depending on the value of the coupling constant. For example, the upper bound of the background value of chameleon field, phi(infinity) < 10(-4)M(Pl), is obtained in the case beta = 1, where beta is the coupling constant between the chameleon field and the matter, and M-Pl is the Planck mass. However, the error of the present data is not so small that we obtain a useful constraint in the case beta = 1/root 6, which corresponds to an f(R) model.

DOI： 10.1103/PhysRevD.86.103503

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

We extend our previous work [Phys. Rev. D 83, 045030 (2011)], which investigated the first-order quantum effect in the Larmor radiation from a moving charge in a spatially homogeneous time-dependent electric field. Specifically, we investigate the quantum Larmor radiation from a moving charge in a monochromatic electromagnetic plane wave background based on the scalar quantum electrodynamics at the lowest order of the perturbation theory. Using the in-in formalism, we derive the theoretical formula of the total radiation energy from a charged particle in the initial states being at rest and being in a relativistic motion. Expanding the theoretical formula in terms of the Planck constant h, we obtain the first-order quantum effect on the Larmor radiation. The quantum effect generally suppresses the total radiation energy compared with the prediction of the classical Larmor formula, which is a contrast to the previous work. The reason is explained by the fact that the radiation from a moving charge in a monochromatic electromagnetic plane wave is expressed in terms of the inelastic collisions between an electron and photons of the background electromagnetic waves.

DOI： 10.1142/S0217751X12501424

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

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

DOI： 10.1088/1475-7516/2012/07/050

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

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

DOI： 10.1103/PhysRevD.85.123503

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

We present a new test of the modified gravity endowed with the Vainshtein mechanism with the density profile of a galaxy cluster halo observed through gravitational lensing. A scalar degree of freedom in the galileon modified gravity is screened by the Vainshtein mechanism to recover Newtonian gravity in high-density regions, however it might not be completely hidden on the outer side of a cluster of galaxies. Then the modified gravity might yield an observational signature in a surface mass density of a cluster of galaxies measured through gravitational lensing, since the scalar field could contribute to the lensing potential. We investigate how the transition in the Vainshtein mechanism affects the surface mass density observed through gravitational lensing, assuming that the density profile of a cluster of galaxies follows the original Navarro-Frenk-White (NFW) profile, the generalized NFW profile and the Einasto profile. We compare the theoretical predictions with observational results of the surface mass density reported recently by other researchers. We obtain constraints on the amplitude and the typical scale of the transition in the Vainshtein mechanism in a subclass of the generalized galileon model.

DOI： 10.1088/1475-7516/2012/05/016

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

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

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

DOI： 10.1103/PhysRevD.85.024023

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

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

DOI： 10.1142/S0218271811020421

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

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

DOI： 10.1088/1475-7516/2011/04/025

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

We investigate the validity of the approximate method to describe a strong gravitational lensing which was extended by Alard on the basis of a perturbative approach to an Einstein ring. Adopting an elliptical Navarro-Frenk-White (NFW) lens model, we demonstrate how the approximate method works, focusing on the shape of the image, the magnification, caustics, and the critical line. Simplicity of the approximate method enables us to investigate the lensing phenomena in an analytic way. We derive simple approximate formulas which characterize a lens system near the Einstein ring.

DOI： 10.1142/S0218271811018834

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

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

DOI： 10.1103/PhysRevD.83.045015

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

First-order quantum correction to the Larmor radiation is investigated on the basis of the scalar QED on a homogeneous background of a time-dependent electric field, which is a generalization of a recent work by Higuchi and Walker so as to be extended for an accelerated charged particle in a relativistic motion. We obtain a simple approximate formula for the quantum correction in the limit of the relativistic motion when the direction of the particle motion is parallel to that of the electric field.

DOI： 10.1103/PhysRevD.83.045030

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

We developed a new method of deconvolving the smearing effect of the survey window in the analysis of the galaxy multipole power spectra from a redshift survey. This method is based on the deconvolution theorem, and is compatible with the use of the fast Fourier transform. It is possible to measure the multipole power spectra deconvolved from the window effect efficiently. Applying this method to the luminous red galaxy sample of the Sloan Digital Sky Survey data release 7 as well as mock catalogues, we demonstrate how the method works properly. By this deconvolution technique, the amplitude of the multipole power spectrum is corrected. Besides, the covariance matrices of the deconvolved power spectra become quite close to the diagonal form. This is also advantageous in the study of the BAO signature.

DOI： 10.1143/PTP.125.187

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

DOI： 10.1103/PhysRevD.81.129903

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

A constraint on the viable f(R) model is investigated by confronting theoretical predictions with the multipole power spectrum of the luminous red galaxy sample of the Sloan Digital Sky Survey, data release 7. We obtain a constraint on the Compton wavelength parameter of the f(R) model on the scales of cosmological large-scale structure. A prospect of constraining the Compton wavelength parameter with a future redshift survey is also investigated. The usefulness of the redshift-space distortion for testing the gravity theory on cosmological scales is demonstrated.

DOI： 10.1103/PhysRevD.81.103517

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

We investigate the linear growth rate of cosmological matter density perturbations in a viable f(R) model both numerically and analytically. We find that the growth rate in the scalar-tensor regime can be characterized by a simple analytic formula. We also investigate a prospect of constraining the Compton wavelength scale of the f(R) model with a future weak lensing survey. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevD.81.043528

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

We determine a constraint on the growth factor by measuring the damping of the baryon acoustic oscillations in the matter power spectrum using the Sloan digital sky survey luminous red galaxy sample. We obtain an effective upper limit on sigma(8)D(1)(z=0.3) using the damping of the baryon acoustic oscillation signature, where sigma(8) is the root mean square overdensity in a sphere of radius 8h(-1) Mpc and D(1)(z) is the growth factor at redshift z. The above result assumes that other parameters are fixed and the cosmology is taken to be a spatially flat cold dark matter universe with the cosmological constant.

DOI： 10.1103/PhysRevD.80.123524

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

We study the spectral tilt of primordial perturbations in Horava-Lifshitz cosmology. The uniform approximation, which is a generalization of the familiar Wentzel-Kramers-Brillouin method, is employed to compute the spectral index both numerically and analytically in a closed form. We clarify how the spectral index depends on the inflation model and parameters in the modified dispersion relation.

DOI： 10.1103/PhysRevD.80.063514

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

We investigate the damping of the baryon acoustic oscillations in the matter power spectrum due to the quasinonlinear clustering and redshift-space distortions by confronting the models with the observations of the Sloan Digital Sky Survey luminous red galaxy sample. The chi-squared test suggests that the observed power spectrum is better matched by models with the damping of the baryon acoustic oscillations rather than the ones without the damping. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevD.79.063512

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

We investigate the damping of the baryon acoustic oscillation (BAO) signature in the matter power spectrum due to the quasi-non-linear clustering of density perturbations. On the basis of the third-order perturbation theory, we construct a fitting formula for the damping in an analytic way. This demonstrates that the damping is closely related to the growth factor and the amplitude of the matter power spectrum. Then, we investigate the feasibility of constraining the growth factor through a measurement of the damping of the BAO signature. An extension of our formula including higher order corrections of density perturbations is also discussed.

DOI： 10.1088/1475-7516/2008/10/031

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

As a test of general relativity on cosmological scales, we measure the gamma parameter for the growth rate of density perturbations using the redshift-space distortion of the luminous red galaxies in the Sloan Digital Sky Survey (SDSS). Assuming the cosmological constant model, which matches the results of the WMAP experiment, we find gamma = 0.62 + 1.8(sigma(8) - 0.8) +/- 0.11 at 1-sigma confidence level, which is consistent with the prediction of general relativity, gamma similar or equal to - 0.55 similar to 0.56. Rather high value of sigma(8)(>= 0.87) is required to be consistent with the prediction of the cosmological DGP model, gamma similar or equal to 0.68.

DOI： 10.1143/PTP.120.609

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

We investigate the wave effect in the gravitational lensing by a black hole with very tiny mass less than 10(-19) M-sun (solar mass), which is called attolensing, motivated by a recent report that the lensing signature might be a possible probe of a modified gravity theory in the braneworld scenario. We focus on the finite source size effect and the effect of the relative motion of the source to the lens, which are influential to the wave effect in the attolensing. Astrophysical condition that the lensed interference signature can be a probe of the modified gravity theory is demonstrated. The interference signature in the microlensing system is also discussed.

DOI： 10.1142/S0217751X08038093

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

An acoustic oscillation of the primeval photon-baryon fluid around the decoupling time imprints a characteristic scale in the galaxy distribution today, known as the baryon acoustic oscillation (BAO) scale. Several ongoing and/or future galaxy surveys aim to detect and precisely determine the BAO scale so as to trace the expansion history of the universe. We consider nonlinear and redshift-space distortion effects on the shifts of the BAO scale in k-space using perturbation theory. The resulting shifts are indeed sensitive to different choices for the definition of the BAO scale, which needs to be kept in mind in the data analysis. We present a toy model to explain the physical behavior of the shifts. We find that the BAO scale defined as in Percival et al. (2007, ApJ, 657, 5 1) indeed shows very small shifts (less than or similar to 1&#37;) relative to the prediction in linear theory in real space. The shifts can be predicted accurately for scales where perturbation theory is reliable.

DOI： 10.1093/pasj/59.6.1049

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

DOI： 10.1103/PhysRevD.76.129901

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

We consider the extent to which future imaging surveys of galaxies can distinguish between dark energy and modified gravity models for the origin of the cosmic acceleration. Dynamical dark energy models may have similar expansion rates as models of modified gravity, yet predict different growth of structure histories. We parametrize the cosmic expansion by the two parameters, w0 and wa, and the linear growth rate of density fluctuations by Linder's γ, independently. Dark energy models generically predict γ≈0.55, while the Dvali-Gabadadze-Porrati (DGP) model γ≈0.68. To determine if future imaging surveys can constrain γ within 20&#37; (or Δγ&lt
0.1), we perform the Fisher matrix analysis for a weak-lensing survey such as the ongoing Hyper Suprime-Cam (HSC) project. Under the condition that the total observation time is fixed, we compute the figure of merit (FoM) as a function of the exposure time texp. We find that the tomography technique effectively improves the FoM, which has a broad peak around texp several∼10min
a shallow and wide survey is preferred to constrain the γ parameter. While Δγ&lt
0.1 cannot be achieved by the HSC weak-lensing survey alone, one can improve the constraints by combining with a follow-up spectroscopic survey like Wide-field Fiber-fed Multi-Object Spectrograph (WFMOS) and/or future cosmic microwave background (CMB) observations. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevD.76.023504

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

We investigate photon emission from a moving particle in an expanding universe. This process is analogous to the radiation from an accelerated charge in the classical electromagnetic theory. Using the framework of quantum field theory in curved spacetime, we demonstrate that the Wentzel-Kramers-Brillouin (WKB) approximation leads to the Larmor formula for the rate of the radiation of energy from a moving charge in an expanding universe. Using exactly solvable models in a radiation-dominated universe and in a Milne universe, we examine the validity of the WKB formula. It is shown that the quantum effect suppresses the radiation energy in comparison with the WKB formula.

DOI： 10.1088/1475-7516/2006/11/013

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

We discuss how the baryon acoustic oscillation (BAO) signatures in the galaxy power spectrum can distinguish between modified gravity and the cosmological constant as the source of cosmic acceleration. To this end we consider a model characterized by a parameter n, which corresponds to the Dvali-Gabadadze-Porrati (DGP) model if n=2 and reduces to the standard spatially flat cosmological constant concordance model for n equal to infinity. We find that the different expansion histories of the modified gravity models systematically shifts the peak positions of BAO. A preliminary analysis using the current SDSS luminous red galaxy (LRG) sample indicates that the original DGP model is disfavored unless the matter density parameter exceeds 0.3. The constraints will be strongly tightened with future spectroscopic samples of galaxies at high redshifts. We demonstrate that WFMOS, in collaboration with other surveys such as Planck, will powerfully constrain modified gravity alternatives to dark energy as the explanation of cosmic acceleration.

DOI： 10.1103/PhysRevD.74.063525

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

We report on a measurement of the quadrupole power spectrum in the two degree field (2dF) QSO redshift (2QZ) survey. The analysis used an algorithm parallel to that for estimating the standard monopole power spectrum Without first requiring computation of the correlation function or the anisotropic power spectrum. The error on the quadrupole spectrum was rather large, but the best-fit value of the bias parameter from the quadrupole spectrum is consistent with that from previous investigations of the 2dF data.

DOI： 10.1093/pasj/58.1.93

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

We investigate the finite source size effect in the context of the wave optics in gravitational lensing. The magnification of an extended source is presented in an analytic manner for the singular isothermal sphere lens model as well as the point mass lens model with the use of the thin lens approximation. The condition that the finite source size effect becomes substantial is demonstrated. As an application, we discuss the possible observational consequences of the finite source size effect on astrophysical systems.

DOI： 10.1088/1475-7516/2006/01/023

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

The statistics of multi-field inflation are investigated using the stochastic approach. We analytically obtain the probability distribution function of fields with the scaling approximation by extending the previous work by Amendola. The non-Gaussian nature of the probability distribution function is investigated by decomposing the fields into the adiabatic and isocurvature components. We find that the non-Gaussianity of the isocurvature component can be large compared with that of the adiabatic component. The adiabatic and isocurvature components may be correlated at nonlinear order in the skewness and kurtosis even if uncorrelated at linear level.

DOI： 10.1088/1475-7516/2005/07/005

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

A possible wave effect in the gravitational lensing phenomenon is discussed. We consider the interference of two coherent gravitational waves of slightly different frequencies from a compact binary, due to the gravitational lensing by a galaxy halo. This system shows the modulation of the wave amplitude. The lensing probability of such the phenomenon is of order 10(-5) for a high-z source, but it may be advantageous to the observation due to the magnification of the amplitude.

DOI： 10.1103/PhysRevD.71.101301

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

We show that the redshift-space quadrupole will be a powerful tool for constraining dark energy even if the baryon oscillations are missing from the monopole power spectrum and bias is scale and time dependent. We calculate the accuracy with which next-generation galaxy surveys such as KAOS will measure the quadrupole power spectrum, which gives the leading anisotropies in the power spectrum in redshift space due to linear velocity, and the so-called "Finger of God" and Alcock-Paczynski effects. Combining the monopole and quadrupole power spectra, in the complete absence of baryon oscillations (Omega(b) = 0), leads to a roughly 500&#37; improvement in constraints on dark energy compared with those from the monopole spectrum alone.

DOI： 10.1103/PhysRevLett.94.051301

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

We revisit the power spectrum analysis of the complete sample of the Two-Degree field (2dF) QSO redshift (2QZ) survey, as a complementary test of the work by Outram et al. A power spectrum consistent with that of the 2QZ group is obtained. Differently from their approach, fitting of the power spectrum is investigated by incorporating the nonlinear effects, the geometric distortion, and the light-cone effect. It is shown that the QSO power spectrum is consistent with a Lambda cold dark matter model with the matter density parameter Omega(m) = 0.2-0.5. Our constraint on the density parameter is rather weaker than that of the 2QZ group. We also show that the constraint slightly depends on equation-of-state parameter w of the dark energy. The constraint on w from the QSO power spectrum is demonstrated, although it is not very tight.

DOI： 10.1086/382496

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

We develop a useful formula for power spectrum analysis for high- and intermediate-redshift galaxy samples, as an extension of the work by Feldman, Kaiser & Peacock. An optimal weight factor, which minimizes the errors of the power spectrum estimator, is obtained so that the light cone effect and redshift-space distortions are incorporated. Using this formula, we assess the feasibility of the power spectrum analysis with the luminous red galaxy (LRG) sample in the Sloan Digital Sky Survey as a probe of the equation of state of the dark energy. Fisher matrix analysis shows that the LRG sample can be sensitive to the equation of state around redshift z = 0.13. It is also demonstrated that the LRG sample can constrain the equation of state with (1sigma) error of 10&#37; level, if other fundamental cosmological parameters are well determined independently. For a useful constraint, we point out the importance of modeling the bias, taking the luminosity dependence into account. We also discuss the optimized strategy to constrain the equation of state using power spectrum analysis. For a sample with a fixed total number of objects, it is most advantageous to have a sample with the mean number density 10(-4) h(3) Mpc(-3) in the range of the redshift 0.4 less than or similar to z less than or similar to 1.

DOI： 10.1086/377488

Language：Japanese  

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

DOI： 10.1103/PhysRevD.68.041302

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

In this paper we emphasize the importance of the Sloan Digital Sky Survey (SDSS) quasi-stellar object (QSO) clustering statistics as a unique probe of the Universe. Because the complete SDSS QSO sample covers a quarter of the observable Universe, cosmological parameters estimated from the clustering statistics have an implication as a test of the cosmological principle, by comparing with those from local galaxies and other cosmological observations. Using an analytical approach to the power spectrum for the QSO sample, we assess the accuracy with which the cosmological parameters can be determined. Arguments based on the Fisher matrix approach demonstrate that the SDSS QSO sample might have a potential to provide useful constraints on the density parameters as well as the cosmic equation of state.

DOI： 10.1046/j.1365-8711.2003.06477.x

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

We obtain constraints on the cosmological density parameters, Omega(m) and Omega(b), by comparing the preliminary measurement of the quasi-stellar object (QSO) power spectrum from the Two-Degree Field (2dF) QSO Redshift (2QZ) survey with results from an analytic technique of power spectrum estimation, described herein. We demonstrate the validity of the analytic approach by comparing the results with the power spectrum of an N -body simulation. We find a better fit to the shape of the QSO power spectrum for low-density models with Omega(m) = 0.1-0.4. We show that a finite baryon fraction Omega(b) /Omega(m) = 0.2, consistent with observations of the cosmic microwave background anisotropies and nucleosynthesis, fits the observational result of the 2QZ survey better, though the constraint is not very tight. By using the Fisher matrix technique, we investigate just how large a survey would be required before a significant constraint on the density parameters could be obtained. We demonstrate that the constraint could be significantly improved if the survey was four times larger.

DOI： 10.1046/j.1365-8711.2002.05575.x

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

We assess the feasibility of probing dark energy with strong gravitational lensing systems. The capability of the method, which depends on the accuracy with which the lensing systems are modeled, is quantitatively investigated using the Fisher-matrix formalism. We show that this method might place useful constraints on the density parameter and the redshift evolution of the dark energy by combining it with a constraint from supernova measurements. For this purpose., the lens potential needs to be precisely reconstructed. Ve determine the required quality of data. We also briefly discuss the optimal strategy to constrain the cosmological parameters using gravitational lensing systems.

DOI： 10.1143/PTP.106.917

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

Motivated by a recent work by Terashima (Phys. Rev. D60, 084001), we revisit the fluctuation-dissipation (FD) relation between the dissipative coefficient of a detector and the vacuum noise of fields in curved space-time. In an explicit manner we show that the dissipative coefficient obtained from classical equations of motion of the detector and the scalar (or Dirac) field satisfies the FD relation associated with the vacuum noise of the held, which demonstrates that Terashima's prescription works properly in the N-dimensional de Sitter space-time. This practice is useful not only to reconfirm the validity of the use of the retarded Green function to evaluate the dissipative coefficient from the classical equations of motion but also to understand why the derivation works properly, which is discussed in connection with previous investigations on the basis of the Kubo-Martin-Schwinger (KMS) condition. Possible application to black hole spacetime is also briefly discussed.

DOI： 10.1142/S0217751X01004244

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

A possible method to reconstruct the cosmic equation of state using strong gravitational lensing systems is proposed. The feasibility of the method is investigated by carrying out the reconstruction on the basis of a simple Monte-Carlo simulation. We show that the method can work and that the cosmic equation of state w(z) can be determined within errors of Deltaw similar to +0.1 - +0.2 when a sufficiently large number of lensing systems (N similar to 20) for z less than or similar to 1 are precisely measured. Statistics of lensed sources in a wide and deep survey like the SDSS are also briefly discussed.

DOI： 10.1143/PTP.105.707

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

We discuss the systematic effects arising from the cosmological redshift space (geometric) distortion on the statistical analysis of the isodensity contour using high-redshift catalogs. In particular, we present a simple theoretical model for isodensity statistics in cosmological redshift space, as a generalization of earlier work by Matsubara. The statistical quantities considered here are the two- and three-dimensional genus of the isodensity contour, the surface area, the length of the contour intersecting with a plane, and the number of crossing points of the isodensity contour on a line. We give useful analytic formulae for the isodensity statistics, which take into account corrections from the geometric distortion, the nonlinear clustering, and the nonlinear velocity distortion phenomenologically. We then demonstrate how the geometric distortion and the nonlinear corrections alter the shapes of the statistical quantities on the basis of plausible cosmological models. Our results show that the nonlinear correction can be sensitive to a choice of the redshift-space coordinate as increasing the redshift. The low-dimensional quantities, such as the two-dimensional genus, systematically yield anisotropy due to the geometric and velocity distortions, and their angle-dependence shows a 10&#37;-20&#37; difference of amplitude. Sensitivities for typical high-redshift samples are estimated in an analytic manner, and the influence of the light-cone effect for the isodensity statistics is also discussed. A simple estimation suggests that the systematic effects of geometric and redshift-space distortions can become comparable to or even dominate the statistical error of deep cluster samples and future high-redshift galaxy surveys. These systematic effects might be a useful tool in probing the cosmological model of our universe.

DOI： 10.1086/319795

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

The feasibility of the geometric test as a probe of the cosmic equation of state of the dark energy is discussed assuming the future Two Degree Field QSO sample. We examine the sensitivity of the QSO two-point correlation functions, which are theoretically computed incorporating the light cone effect and the redshift distortions, as well as the nonlinear effect, to a bias model whose evolution is phenomenologically parameterized. It is shown that the correlation functions are sensitive to a mean amplitude of the bias and not to the speed of the redshift evolution. We will also demonstrate that an optimistic geometric test could suffer from the possibility that a signal from the cosmological model can be confused with that from a stochastic character of the bias.

DOI： 10.1086/319135

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

The evolution of baryon density perturbations on very small scales is investigated. In particular, the nonlinear growth induced by the radiation drag force from the shear velocity field on larger scales during the recombination epoch, originally proposed by Shaviv in 1998, is studied in detail. We find that inclusion of the diffusion term, which Shaviv neglected in his analysis, results in rather mild growth with growth factor <<100, instead of the enormous amplification, similar to 10(4), of Shaviv's original claim, since the diffusion suppresses the growth. The growth factor strongly depends on the amplitude of the large-scale velocity field. The nonlinear growth mechanism is applied to density perturbations of general adiabatic cold dark matter (CDM) models. For these models, it has been found in previous works that the baryon density perturbations are not completely erased by diffusion damping if there are gravitational potential perturbations from the CDM component. Employing the perturbed rate equation derived in this paper, the nonlinear evolution of baryon density perturbations is investigated. We find that : (1) The nonlinear growth is larger for smaller scales. This mechanism only affects perturbations whose scales are smaller than similar to 10(2) M-., comparable to stellar scales. (2) The maximum growth factors of baryon density fluctuations for various COBE-normalized CDM models are typically less than a factor of 10 for 3 sigma large-scale velocity peaks. (3) The growth factor depends on Omega (b).

DOI： 10.1086/318352

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

We examine the effects of the linear and the cosmological redshift-space distortions on the power spectrum of cosmological objects on a light cone. We develop theoretical formulae for the power spectrum in linear theory of density perturbations in a rigorous manner starting from a first principle corresponding to Fourier analysis. Approximate formulae, which are useful properly to incorporate the redshift-space distortion effects into the power spectrum, are derived, and the validity is examined. Applying our formulae to galaxy and quasar samples that roughly match the Sloan Digital Sky Survey, we will show how the redshift-space distortions distort the power spectrum on the light cone quantitatively.

DOI： 10.1086/313381

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

We have developed a model to describe two-point correlation functions of clusters of galaxies in X-ray flux limited surveys. Our model properly takes into account nonlinear gravitational evolution of mass fluctuations, redshift-space distortion due to linear peculiar velocity fields and to fingers-of-god, cluster abundance, and bias evolution on the basis of the Press-Schechter theory, the light-cone effect, and the selection function due to the X-ray flux, temperature, and luminosity limits. Applying this model in representative cosmological models, we present quantitative predictions for X-ray-selected samples that should be feasible from future surveys with the X-ray satellites, including Astro-E, Chandra, and XMM. The comparison of these predictions and the observed cluster clustering will generate important cosmological constraints that complement the duster abundance and the cosmic microwave background.

DOI： 10.1086/308778

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

We present a theoretical formalism to predict two-point clustering statistics (the power spectrum and the two-point correlation function), which simultaneously takes account of the linear velocity distortion, the nonlinear velocity distortion (finger-of-god), the cosmological redshift-space distortion, and the light-cone effect. To demonstrate the importance of these effects in exploring the clustering of objects at high redshifts, we show several model predictions for magnitude-limited surveys of galaxies and quasars. This methodology provides a quantitative tool to test various theoretical models against the upcoming precision data on clustering in the universe.

DOI： 10.1093/pasj/52.2.249

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

We present a theoretical formalism to predict two-point clustering statistics (the power spectrum and the two-point correlation function), which simultaneously takes account of the linear velocity distortion, the nonlinear velocity distortion (finger-of-god), the cosmological redshift-space distortion, and the light-cone effect. To demonstrate the importance of these effects in exploring the clustering of objects at high redshifts, we show several model predictions for magnitude-limited surveys of galaxies and quasars. This methodology provides a quantitative tool to test various theoretical models against the upcoming precision data on clustering in the universe.

DOI： 10.1093/pasj/52.2.249

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

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

宇宙論的赤方偏移歪みを用いた宇宙モデルのテスト(宇宙論的幾何学テスト)において考慮すべき観測的効果を取り上げ解説しながら、このテストの問題点について再考する。光円錐効果まで考慮した相関関数の理論的表式を導出し、2dFのクェーサー・サンプルを想定した相関関数の振舞いを定量的に調べる。特に、バイアスの不定性に着目し、バイアスの進化がどの程度相関関数の理論的予言に影響するかについて定量的な議論を試みる。

DOI： 10.24532/soken.101.6_F4

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

Cosmological Light-Cone Effect on the Power Spectrum of Galaxies and Quasars in Wide-Field Redshift Surveys

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

Two-point correlation functions of high-redshift objects; an explicit formulation on a light-cone hypersurface
While all the cosmological observations are carried out on a light cone, the null hypersurface of an observer at z = 0, the clustering statistics has been properly defined only on the constant-time hypersurface. We develop a theoretical formulation for a two-point correlation function on the light cone and derive a practical approximate expression relevant to the discussion of clustering of high-redshift objects at large separations. As a specific example, we present predictions of the two-point correlation function for the Durham/AAT, SDSS, and 2dF quasar catalogues. We also briefly discuss the effects of adopted luminosity function, cosmological parameters, and bias models on the correlation function on the light cone.

DOI： 10.1086/307184

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

Two-Point Correlation Function of High-Redshift Objects on a Light-Cone ;Effect of the Linear Redshift-Space Distortion
A theoretical formulation for the two-point correlation function on a light cone is developed in red-shift space. On the basis of the previous work by Yamamoto & Suto, in which a theoretical formula for the two-point correlation function on a light cone has been developed in real space, we extend it to the formula in redshift space by taking the peculiar velocity of the sources into account. A simple expression for the two-point correlation function is derived. We briefly discuss QSO correlation functions on a light cone adopting a simple model of the sources.

DOI： 10.1086/307492

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

Chiral phase transitions driven by space-time curvature effects are investigated in de Sitter space in the supersymmetric Nambu–Jona-Lasinio model with soft supersymmetry breaking. The model is considered to be suitable for the analysis of possible phase transitions in inflationary universe. It is found that a restoration of the broken chiral symmetry takes place in two patterns for increasing curvature: the first-order and second-order phase transition, respectively, depending on initial settings of the four-body interaction parameter and the soft supersymmetry breaking parameter. The critical curves expressing the phase boundaries in these parameters are obtained. Cosmological implications of the result are discussed in connection with bubble formations and the creation of cosmic strings during the inflationary era. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevD.59.101302

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

DOI： 10.1143/PTPS.133.183

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

Small-scale fluctuations in cosmic X-ray background ; A power spectrum approach

DOI： 10.1103/PhysRevD.58.103508

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

Evolution of Small Scale Cosmological Baryon Perturbations and Matter Transfer Functions
The evolution of small-scale cosmological perturbations is carefully reexamined. Through interactions with photons via electrons, baryon perturbations show interesting behavior on some physical scales. Characteristic features of the evolution of baryon density fluctuations are discussed. In CDM models, a power-law growing phase of the small-scale baryon density fluctuations is found, characterized by a terminal velocity after the diffusion (Silk) damping and before the decoupling epoch. A transfer function for total matter-density fluctuations is then studied by taking those physical processes into account. We present an analytic transfer function as a function of redshift z that is applicable for the entire range up to a solar-mass scale in the high-z universe, and that is also suitable for high baryon fraction models.

DOI： 10.1086/305841

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

Boltzmann approach to the large-angle cosmic X-ray background fluctuations

DOI： 10.1046/j.1365-8711.1998.01647.x

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

DOI： 10.1143/PTP.99.237

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

On the Cosmic X-ray Background Fluctuations

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

DOI： 10.1103/PhysRevD.56.7566

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

DOI： 10.1086/177295

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

Quantum excitations of intrinsic degrees of freedom in multi-dimensional tunneling system

DOI： 10.1143/PTP.96.1147

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

Quantum fluctuations and CMB anisotropies in one bubble inflationary models

DOI： 10.1103/PhysRevD.54.5031

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

DOI： 10.1103/PhysRevD.53.2045

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

Euclidean Vacuum mode function in an open slicing chart of de Sitter spacetime

DOI： 10.1103/PhysRevD.51.2979

Other Link： https://journals.aps.org/prd/pdf/10.1103/PhysRevD.51.2979

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

Particle Spectrum Created through Bubble Nucleation and Quantum Field Theory in the Milne Universe

DOI： 10.1103/PhysRevD.51.2968

Other Link： https://doi.org/10.1103/PhysRevD.51.2968

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

Skewness of Cosmic Microwave Background Anisotropy in an Inflationary Isocurvature Baryon Model

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

Probability distribution functional in curved spaectime

DOI： 10.1142/S0217751X9400011X

Other Link： https://www.worldscientific.com/doi/abs/10.1142/S0217751X9400011X

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

Field Theoretical Description of Quantum Fluctuation in Multi-dimensional Approach

DOI： 10.1103/PhysRevD.49.1039

Other Link： https://journals.aps.org/prd/pdf/10.1103/PhysRevD.49.1039

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

Quantum state during and after nucleation of an O(4)-symmetric bubble

DOI： 10.1143/ptp/90.5.1019

Other Link： https://academic.oup.com/ptp/article/90/5/1019/1883964

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

Quantum Tunneling in Multidimensional tunneling systems

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

DOI： 10.1088/0264-9381/10/5/003

Other Link： https://iopscience.iop.org/article/10.1088/0264-9381/10/5/003/pdf

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

Quantum state inside a vacuum bubble and creation of an open universe

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

Superexpansionary divergence

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

We present the analytic solution of N Einstein-Rosen bridges (''N black holes'') in the space-time with a cosmological constant LAMBDA and analyze it for one- and two-bridge systems. We discuss the three kinds of apparent horizons: i.e., the black-hole, white-hole, and cosmological apparent horizons. In the case of two Einstein-Rosen bridges, when the ''total mass'' is larger than a critical value, the black-hole apparent horizon surrounding two Einstein-Rosen bridges is not formed even if the distance is very short. Furthermore, in this case, the cosmological apparent horizon enclosing both bridges does not appear. Hence, it seems that when the ''total mass'' is very large, the Einstein-Rosen bridges cannot collapse into one black hole unless the ''gravitational mass'' is released in some way.

Other Link： https://doi.org/10.1103/PhysRevD.47.3203

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

DOI： 10.1103/PhysRevD.46.4206

Other Link： https://doi.org/10.1103/PhysRevD.46.4206

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

Motion of a Spherical Domain Wall and the Large-Scale Structure Formation

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：神戸コンベンションセンター (オンライン)   Country：Japan  

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：KEK, Tsukuba   Country：Japan  

Event date： 2022.10 - 2022.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：online   Country：Japan  

Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Venue：online   Country：Japan  

Event date： 2022.5

Language：Japanese  

Venue：online   Country：Japan  

Event date： 2022.3 - 2022.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2022.2

Language：English   Presentation type：Oral presentation (general)  

Venue：KEK（オンライン）   Country：Japan  

Other Link： https://www-conf.kek.jp/joint-colloquium/

Event date： 2021.10

Language：Japanese  

Venue：京都大学基礎物理学研究所（京都）   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

ビッグバン宇宙は、1964 年にペンジアスとウィルソンによって宇宙マイクロ波背景放射が発見されてか ら本格的な研究が始まりました。ジェームズ・ピーブルズは、その前後から宇宙の物理的進化の研究を 一貫して進め、現代宇宙論の理論的枠組みの確立に大きな貢献をしました。特に、宇宙マイクロ波背景 放射と銀河形成の関係の重要性を 1965 年の論文で述べており、物理的宇宙論の始まりと評されていま す。膨張宇宙における密度揺らぎの成長や相関関数を用いた銀河分布の統計的記述の理論的定式化を確 立し、また早くから暗黒物質や宇宙項の重要性も指摘しています。ピーブルズの研究業績は、単著論文 として発表されている先駆的な論文が多く、現代の宇宙論はピーブルズの研究の延長線上に発展してき たと言っても良いかもしれません。本講演では、この物理的宇宙論の発展と今後の展望について解説し ます。

Event date： 2019.11 - 2020.11

Language：English  

Venue：Kobe University   Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Event date： 2019.5

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Type：Competition, symposium, etc. 

Number of participants：184