83 citations · 400 across the 18 of their papers we have counts for
8 papers · 1 filter
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…
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…
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…
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…