59 citations · 156 across the 12 of their papers we have counts for
6 papers · 1 filter
Parity violation in primordial tensor non-Gaussianities from matter bounce cosmology
Shingo Akama, Mian Zhu
It has been shown that primordial tensor non-Gaussianities from a cubic Weyl action with a non-dynamical coupling are suppressed by the so-called slow-roll parameter in a conventio…
Imprints of primordial gravitational waves with non-Bunch-Davies initial states on CMB bispectra
Shingo Akama, Hiroaki W. H. Tahara
It has been shown that both scalar and tensor modes with non-Bunch-Davies initial states can enhance the amplitudes of the primordial bispectra compared to those with the Bunch-Dav…
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…
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…
General theory of cosmological perturbations in open and closed universes from the Horndeski action
Shingo Akama, Tsutomu Kobayashi
Our Universe is nearly spatially flat, but this does not mean that it is exactly spatially flat. In this paper we derive general quadratic actions for cosmological perturbations in…