Density Fluctuations in Thermal Inflation and Non-Gaussianity (2009)
Kawasaki, Masahiro, Takahashi, Tomo, Yokoyama, Shuichiro
We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 $e$-folds after the standard inflation, the time of horizon-exit during inflation...
Primordial Non-Gaussianity in Models with Dark Matter Isocurvature Fluctuations (2009)
Takahashi, Tomo, Yamaguchi, Masahide, Yokoyama, Shuichiro
We investigate primordial non-Gaussianity and dark matter isocurvature fluctuations in the modulated reheating and the curvaton scenarios. In these scenarios, large non-Gaussianity can be generated,...
Gravitino Dark Matter and Non-Gaussianity (2009)
Takahashi, Tomo, Yamaguchi, Masahide, Yokoyama, Jun'ichi, Yokoyama, Shuichiro
We investigate density fluctuations in a scenario with gravitino dark matter in the framework of modulated reheating, which is known to generate large non-Gaussianity. We show that gravitino dark...
Phenomenological Aspects of Horava-Lifshitz Cosmology (2009)
Mukohyama, Shinji, Nakayama, Kazunori, Takahashi, Fuminobu, Yokoyama, Shuichiro
We show that, assuming the dispersion relation proposed recently by Horava in the context of quantum gravity, radiation energy density exhibits a peculiar dependence on the scale factor; the...
Gravitational waves from p-form inflation (2009)
Kobayashi, Tsutomu, Yokoyama, Shuichiro
Recently it was shown that an inflationary background can be realized by any $p$-form field non-minimally coupled to gravity. In this paper, we study gravitational waves generated during p-form...
Yokoyama, Shuichiro, Suyama, Teruaki, Tanaka, Takahiro
We present a new efficient method for computing the non-linearity parameters of the higher order correlation functions of local type curvature perturbations in inflation models having a $\cal...
Anisotropic Inflation from Vector Impurity (2008)
Kanno, Sugumi, Kimura, Masashi, Soda, Jiro, Yokoyama, Shuichiro
We study an inflationary scenario with a vector impurity. We show that the universe undergoes anisotropic inflationary expansion due to a preferred direction determined by the vector. Using the...
Primordial statistical anisotropy generated at the end of inflation (2008)
Yokoyama, Shuichiro, Soda, Jiro
We present a new mechanism for generating primordial statistical anisotropy of curvature perturbations. We introduce a vector field which has a non-minimal kinetic term and couples with a waterfall...
Primordial Non-Gaussianity in Multi-Scalar Inflation (2007)
Yokoyama, Shuichiro, Suyama, Teruaki, Tanaka, Takahiro
We give a concise formula for the non-Gaussianity of the primordial curvature perturbation generated on super-horizon scales in multi-scalar inflation model without assuming slow-roll conditions....
Primordial Non-Gaussianity in Multi-Scalar Slow-Roll Inflation (2007)
Yokoyama, Shuichiro, Suyama, Teruaki, Tanaka, Takahiro
We analyze the non-Gaussianity for primordial curvature perturbations generated in multi-scalar slow-roll inflation model including the model with non-separable potential by making use of $\delta N$...
Generating the primordial curvature perturbations in preheating (2006)
Suyama, Teruaki, Yokoyama, Shuichiro
We show that the primordial curvature perturbations may originate not from the quantum fluctuations of inflaton during inflation but from isocurvature perturbations which are amplified during...
Wronskian Formulation of the Spectrum of Curvature Perturbations (2006)
Yokoyama, Shuichiro, Tanaka, Takahiro, Sasaki, Misao, Stewart, Ewan D.
We present a new formulation for the evaluation of the primordial spectrum of curvature perturbations generated during inflation, using the fact that the Wronskian of the scalar field perturbation...
A New delta N Formalism for Multi-Component Inflation (2005)
Lee, Hyun-Chul, Sasaki, Misao, Stewart, Ewan D., Tanaka, Takahiro, Yokoyama, Shuichiro
The delta N formula that relates the final curvature perturbation on comoving slices to the inflaton perturbation on flat slices after horizon crossing is a powerful and intuitive tool to compute the...