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Kazuhiro Yamamoto Last modified date：2022.06.16

Professor / Fundamental particle physics / Department of Physics / Faculty of Sciences


Papers
1. Masahiro Hotta, Yasusada Nambu, Yuuki Sugiyama, Kazuhiro Yamamoto, Go Yusa , Expanding edges of quantum Hall systems in a cosmology language: Hawking radiation from de Sitter horizon in edge modes, PHYSICAL REVIEW D, https://doi.org/10.1103/PhysRevD.105.105009, 105, 105009-1 -105009-14, 2022.05, [URL], 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 two-dimensional 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 Gibbons-Hawking temperature from the future de Sitter horizon formed in the expanding-edge region..
2. Kazushige Ueda, Atsushi Higuchi, Kazuhiro Yamamoto, Ar Rohim, Yue Nan, Entanglement of the vacuum between left, right, future, and past: Dirac spinor in Rindler and Kasner spaces, PHYSICAL REVIEW D, 10.1103/PhysRevD.103.125005, 103, 125005-1-125005-23, 2021.06, [URL].
3. Yuuki Sugiyama, Kazuhiro Yamamoto, Tsutomu Kobayashi, Gravitational waves in Kasner spacetimes and Rindler wedges in Regge-Wheeler gauge: Formulation of Unruh effect, Physical Review D, 10.1103/PhysRevD.103.026017, 103, 083503-1, 2021.04, [URL].
4. Daisuke Miki, Akira Matsumura, Kazuhiro Yamamoto, Entanglement and decoherence of massive particles due to gravity, PHYSICAL REVIEW D, 10.1103/PhysRevD.103.026017, 103, 2, 2021.01, [URL].
5. Akira Matsumura, Kazuhiro Yamamoto , Gravity-induced entanglement in optomechanical systems, PHYSICAL REVIEW D, 10.1103/PhysRevD.102.106021, 102, 10, 2020.11, [URL].
6. Yue Nan, Kazuhiro Yamamoto, Hajime Aoki, Satoshi Iso, and Daisuke Yamauchi, Large-scale inhomogeneity of dark energy produced in the ancestor vacuum, PHYSICAL REVIEW D, 10.1103/PhysRevD.99.103512, 99, 10, 2019.05, 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..
7. Tatsuro Kanemaru, Chiaki Hikage, Gert Huesi, Ayumu Terukina, Kazuhiro Yamamoto, What can we learn from higher multipole power spectra of galaxy distribution in redshift space?, PHYSICAL REVIEW D, 10.1103/PhysRevD.92.023523, 92, 2, 2015.07, 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..
8. Rampei Kimura, Tsutomu Kobayashi, Kazuhiro Yamamoto, Vainshtein screening in a cosmological background in the most general second-order scalar-tensor theory, PHYSICAL REVIEW D, 10.1103/PhysRevD.85.024023, 85, 2, 2012.01, 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..
9. Y Suto, H Magira, K Yamamoto, Light-cone effect on clustering statistics in cosmological redshift space, PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN, 10.1093/pasj/52.2.249, 52, 2, 249-257, 2000.04, 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..
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12. Skewness of CMB Anisotropies in an Inflationary Isocurvature Baryon Model
We investigate the cosmic variance of the skewness of the cosmic microwave

background (CMB) anisotropies in an inflationary model which leads to the

baryon isocurvature scenario for the cosmic structure formation. In this model,

the baryon number fluctuations are given by a sinusoidal function of a random

Gaussian field. We find that the skewness is very small in comparison with that

of the fluctuations which obey Gaussian statistics..
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