83 citations · 400 across the 18 of their papers we have counts for
18 papers
Abundance of cosmic voids in EFT of dark energy
Toshiki Takadera, Shin'ichi Hirano, Tsutomu Kobayashi
Cosmic voids in the large-scale structure are among the useful probes for testing gravity on cosmological scales. In this paper, we investigate the evolution of voids in the Hornde…
Stochastic gravitational wave background anisotropies from inflation with non-Bunch-Davies states
Shingo Akama, Shin'ichi Hirano, Shuichiro Yokoyama
It is known that stochastic gravitational wave backgrounds (SGWBs) have anisotropies generated by squeezed-type tensor non-Gaussianities originating from scalar-tensor-tensor (STT)…
First test of the consistency relation for the large-scale structure using the anisotropic three-point correlation function of BOSS DR12 galaxies (An explanatory video is available at https://youtu.be/Zi36ooLPhss.)
Naonori S. Sugiyama, Daisuke Yamauchi, Tsutomu Kobayashi +6
We present, for the first time, an observational test of the consistency relation for the large-scale structure (LSS) of the Universe through a joint analysis of the anisotropic tw…
New constraints on cosmological modified gravity theories from anisotropic three-point correlation functions of BOSS DR12 galaxies
Naonori S. Sugiyama, Daisuke Yamauchi, Tsutomu Kobayashi +6
We report a new test of modified gravity theories using the large-scale structure of the Universe. This paper is the first attempt to (1) apply a joint analysis of the anisotropic…
Cosmological gravity probes: connecting recent theoretical developments to forthcoming observations
Shun Arai, Katsuki Aoki, Yuji Chinone +20
Since the discovery of the accelerated expansion of the present Universe, significant theoretical developments have been made in the area of modified gravity. In the meantime, cosm…
Primordial non-Gaussianity from Galilean Genesis without strong coupling problem
Shingo Akama, Shin'ichi Hirano
Galilean Genesis is generically plagued with a strong coupling problem, but this can be avoided depending on the hierarchy between a classical energy scale of genesis and a strong…
Effective Field Theory of Large Scale Structure in modified gravity and application to Degenerate Higher-Order Scalar-Tensor theories
Shin'ichi Hirano, Tomohiro Fujita
In modified gravity, the one-loop matter power spectrum exhibits an ultraviolet divergence as shown in the framework of the degenerate higher-order scalar-tensor theory. To address…
Primordial black hole formation from massless scalar isocurvature
Chul-Moon Yoo, Tomohiro Harada, Shin'ichi Hirano +2
We numerically study the primordial black hole (PBH) formation by an isocurvature perturbation of a massless scalar field on super Hubble scales in the radiation-dominated universe…
Gravitational positivity bounds
Junsei Tokuda, Katsuki Aoki, Shin'ichi Hirano
We study the validity of positivity bounds in the presence of a massless graviton, assuming the Regge behavior of the amplitude. Under this assumption, the problematic -channel…
UV sensitive one-loop matter power spectrum in degenerate higher-order scalar-tensor theories
Shin'ichi Hirano, Tsutomu Kobayashi, Daisuke Yamauchi +1
We study matter density perturbations up to third order and the one-loop matter power spectrum in degenerate higher-order scalar-tensor (DHOST) theories beyond Horndeski. We system…
Abundance of Primordial Black Holes in Peak Theory for an Arbitrary Power Spectrum
Chul-Moon Yoo, Tomohiro Harada, Shin'ichi Hirano +1
We modify the procedure to estimate PBH abundance proposed in arXiv:1805.03946 so that it can be applied to a broad power spectrum such as the scale-invariant flat power spectrum.…
Primordial tensor non-Gaussianities from general single-field inflation with non-Bunch-Davies initial states
Shingo Akama, Shin'ichi Hirano, Tsutomu Kobayashi
It has been found that the primordial non-Gaussianity of the curvature perturbation in the case of non-Bunch-Davies initial states can be enhanced compared with those in the case o…
Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem
Shingo Akama, Shin'ichi Hirano, Tsutomu Kobayashi
It has been pointed out that matter bounce cosmology driven by a k-essence field cannot satisfy simultaneously the observational bounds on the tensor-to-scalar ratio and non-Gaussi…
On the screening mechanism in DHOST theories evading gravitational wave constraints
Shin'ichi Hirano, Tsutomu Kobayashi, Daisuke Yamauchi
We consider a subclass of degenerate higher-order scalar-tensor (DHOST) theories in which gravitational waves propagate at the speed of light and do not decay into scalar fluctuati…
Constraining DHOST theories with linear growth of matter density fluctuations
Shin'ichi Hirano, Tsutomu Kobayashi, Daisuke Yamauchi +1
We investigate the potential of cosmological observations, such as galaxy surveys, for constraining degenerate higher-order scalar-tensor (DHOST) theories, focusing in particular o…
Matter bispectrum beyond Horndeski
Shin'ichi Hirano, Tsutomu Kobayashi, Hiroyuki Tashiro +1
The Horndeski scalar-tensor theory and its recent extensions allow nonlinear derivative interactions of the scalar degree of freedom. We study the matter bispectrum of large scale…
Healthy imperfect dark matter from effective theory of mimetic cosmological perturbations
Shin'ichi Hirano, Sakine Nishi, Tsutomu Kobayashi
We study the stability of a recently proposed model of scalar-field matter called mimetic dark matter or imperfect dark matter. It has been known that mimetic matter with higher de…
Ultra slow-roll G-inflation
Shin'ichi Hirano, Tsutomu Kobayashi, Shuichiro Yokoyama
The conventional slow-roll approximation is broken in the so-called "ultra slow-roll" models of inflation, for which the inflaton potential is exactly (or extremely) flat. The inte…