研究者詳細 - 泉　圭介

Renormalized newtonian cosmic evolution with primordial non-gaussianity

その他リンク： http://arxiv.org/pdf/0712.0902v3

Massive spin-2 ghost in de sitter spacetime

K. Izumi, K. Koyama, O. Pujolas, T. Tanaka

Proceedings of the 18th Workshop on General Relativity and Gravitation in Japan, JGRG 2008 2008年

Izumi K., Soda J.

Proceedings of the 17th Workshop on General Relativity and Gravitation in Japan, JGRG 2007 頁： 153 - 156 2007年12月

出版者・発行元：Proceedings of the 17th Workshop on General Relativity and Gravitation in Japan, JGRG 2007

We study Newtonian cosmological perturbation theory from a field theoretical point of view. We derive a path integral representation for the cosmological evolution of stochastic fluctuations. Our main result is the closed form of the generating functional valid for any initial statistics. Moreover, we extend the renormalization group method proposed by Mataresse and Pietroni to the case of primordial non-Gaussian density and velocity fluctuations. As an application, we calculate the nonlinear propagator and examine how the non-Gaussianity affects the memory of cosmic fields to their initial conditions. It turns out that the non-Gaussianity affect the nonlinear propagator. In the case of positive skewness, the onset of the nonlinearity is advanced with a given comoving wavenumber. On the other hand, the negative skewness gives the opposite result.

Bubbles in the self-accelerating universe 査読有り国際誌 Open Access

Izumi, K; Koyama, K; Pujolàs, O; Tanaka, T

PHYSICAL REVIEW D 76 巻 ( 10 ) 2007年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

We revisit the issue of the stability in the Dvali-Gabadadze-Porrati model by considering the nucleation of bubbles of the conventional branch within the self-accelerating branch. We construct an instanton describing this process in the thin wall approximation. On one side of the bubble wall, the bulk consists of the exterior of the brane, while on the other side it is the interior. The solution requires the presence of a 2-brane (the bubble wall) which induces the transition. However, we show that this instanton cannot be realized as the thin wall limit of any smooth solution. Once the bubble thickness is resolved, the equations of motion do not allow O(4) symmetric solutions joining the two branches. We conclude that the thin wall instanton is unphysical, and that one cannot have processes connecting the two branches, unless negative tension bubble walls are introduced. This also suggests that the self-accelerating branch does not decay into the conventional branch nucleating bubbles. We comment on other kinds of bubbles that could interpolate between the two branches. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevD.76.104041

その他リンク： http://arxiv.org/pdf/0706.1980v1

Renormalized Newtonian cosmic evolution with primordial non-Gaussianity 査読有り国際誌

Izumi, K; Soda, J

PHYSICAL REVIEW D 76 巻 ( 8 ) 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review D - Particles, Fields, Gravitation and Cosmology

We study Newtonian cosmological perturbation theory from a field theoretical point of view. We derive a path integral representation for the cosmological evolution of stochastic fluctuations. Our main result is the closed form of the generating functional valid for any initial statistics. Moreover, we extend the renormalization group method proposed by Mataresse and Pietroni to the case of primordial non-Gaussian density and velocity fluctuations. As an application, we calculate the nonlinear propagator and examine how the non-Gaussianity affects the memory of cosmic fields to their initial conditions. It turns out that the non-Gaussianity affects the nonlinear propagator. In the case of positive skewness, the onset of the nonlinearity is advanced with a given comoving wave number. On the other hand, the negative skewness gives the opposite result. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevD.76.083517

その他リンク： http://arxiv.org/pdf/0706.1604v2

Unexorcized ghost in DGP brane world 査読有り国際誌 Open Access

Izumi, K; Tanaka, T; Koyama, K

JOURNAL OF HIGH ENERGY PHYSICS 2007 巻 ( 4 ) 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of High Energy Physics

The brane world model proposed by Dvali-Gabadadze-Porrati realizes self-acceleration of the universe. However, it is known that this cosmological solution contains a spin-2 ghost. We study the possibility of avoiding the appearance of the ghost by slightly modifying the model via the introduction of a second brane. First, we consider a simple model without stabilization of the brane separation. By changing the separation between the branes, we find that we can erase the spin-2 ghost. However, this can be done only at the expense of the appearance of a spin-0 ghost instead. We discuss why these two different types of ghosts are correlated. Then, we examine a model with stabilization of the brane separation. Even in this case, we find that the correlation between spin-0 and spin-2 ghosts remains. As a result we find that we cannot avoid the appearance of a ghost by introducing a second brane in the model. © SISSA 2007.

DOI： 10.1088/1126-6708/2007/04/053

Unexorcized ghost in DGP brane world

その他リンク： http://arxiv.org/pdf/hep-th/0610282v3

Izumi K., Koyama K., Tanaka T.

Proceedings of the 16th Workshop on General Relativity and Gravitation in Japan, JGRG 2006 頁： 267 - 270 2006年12月

出版者・発行元：Proceedings of the 16th Workshop on General Relativity and Gravitation in Japan, JGRG 2006

The braneworld model of Dvali-Gabadadze-Porrati realizes the self-accelerating universe. However, it is known that this cosmological solution contains a spin-2 ghost. We study the possibility of avoiding the appearance of the ghost by slightly modifying the model, introducing the second brane. First we consider a simple model without stabilization of the separation of the brane. By changing the separation between the branes, we find we can erase the spin-2 ghost. However, this can be done only at the expense of the appearance of a spin-0 ghost instead. We discuss why these two different types of ghosts are correlated. Then, we examine a model with stabilization of the brane separation. Even in this case, we find that the correlation between spin-0and spin-2 ghosts remains. As a result we find we cannot avoid the appearance of ghost by two-branes model.

The avoidance of the ghost problem in the DGP brane world: Two-branes model

Izumi K., Tanaka T.

Proceedings of the 15th Workshop on General Relativity and Gravitation in Japan, JGRG 2005 頁： 135 - 138 2005年12月

出版者・発行元：Proceedings of the 15th Workshop on General Relativity and Gravitation in Japan, JGRG 2005

We discuss gravitational perturbations of de Sitter brane world in the DGP model. In the original DGP model with a self-Accelerating single brane, a ghost-like field appeal's, which is thought to be problematic. To cure this ghost problem keeping the advantage of the self-Acceleration, we propose a two-branes model, which has another boundary brane in the bulk. When the new boundary brane is sufficiently close to the original brane, there is no ghost in this model. Moreover, when the acceleration of the universe is solely due to the modification of gravity without the aid of dark energy, the model is free from ghost irrespective of the position of the new boundary brane.