Cosmological Magnetic Fields from Inflation and Backreaction (2009)
Kanno, Sugumi, Soda, Jiro, Watanabe, Masa-aki
We study the backreaction problem in a mechanism of magnetogenesis from inflation. In usual analysis, it has been assumed that the backreaction due to electromagnetic fields spoils inflation once it...
Holographic Superconductors with Higher Curvature Corrections (2009)
Gregory, Ruth, Kanno, Sugumi, Soda, Jiro
We study (3+1)-dimensional holographic superconductors in Einstein-Gauss-Bonnet gravity both numerically and analytically. It is found that higher curvature corrections make condensation harder. We...
Instability of Small Lovelock Black Holes in Even-dimensions (2009)
Takahashi, Tomohiro, Soda, Jiro
We study the stability of static black holes in Lovelock theory which is a natural higher dimensional generalization of Einstein theory. We derive a master equation for tensor perturbations in...
Einstein-Maxwell-Dilaton theories with a Liouville potential (2009)
Charmousis, Christos, Gouteraux, Blaise, Soda, Jiro
We find and analyse solutions of Einstein's equations in arbitrary d dimensions and in the presence of a scalar field with a Liouville potential coupled to a Maxwell field. We consider spacetimes of...
Chiral Primordial Gravitational Waves from a Lifshitz Point (2009)
Takahashi, Tomohiro, Soda, Jiro
We study primordial gravitational waves produced during inflation in quantum gravity at a Lifshitz point proposed by Ho${\rm\check{r}}$ava. Assuming power-counting renormalizability, foliation...
Stability of Lovelock Black Holes under Tensor Perturbations (2009)
Takahashi, Tomohiro, Soda, Jiro
We study the stability of static black holes in the third order Lovelock theory. We derive a master equation for tensor perturbations. Using the master equation, we analyze the stability of Lovelock...
Watanabe, Masa-aki, Kanno, Sugumi, Soda, Jiro
We study an inflationary scenario with a vector field coupled with an inflaton field. We show that the inflationary universe is endowed with anisotropic hair for a wide range of coupling functions....
Looking at the Gregory-Laflamme instability through quasi-normal modes (2008)
Konoplya, R. A., Murata, Keiju, Soda, Jiro, Zhidenko, A.
We study evolution of gravitational perturbations of black strings. It is well known that for all wavenumber less than some threshold value, the black string is unstable against scalar type of...
Higher Curvature Corrections to Primordial Fluctuations in Slow-roll Inflation (2008)
We study higher curvature corrections to the scalar spectral index, the tensor spectral index, the tensor-to-scalar ratio, and the polarization of gravitational waves. We find that the higher...
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...
Stability of Five-dimensional Myers-Perry Black Holes with Equal Angular Momenta (2008)
We study the stability of five-dimensional Myers-Perry black holes with equal angular momenta which have an enlarged symmetry, U(2). Using this symmetry, we derive master equations for a part of...
Evolution of perturbations of squashed Kaluza-Klein black holes: escape from instability (2008)
Ishihara, Hideki, Kimura, Masashi, Konoplya, Roman A., Murata, Keiju, Soda, Jiro, Zhidenko, Alexander
The squashed Kaluza-Klien (KK) black holes differ from the Schwarzschild black holes with asymptotic flatness or the black strings even at energies for which the KK modes are not excited yet, so that...
On the Stability of Squashed Kaluza-Klein Black Holes (2007)
Kimura, Masashi, Murata, Keiju, Ishihara, Hideki, Soda, Jiro
The stability of squashed Kaluza-Klein black holes is studied. The squashed Kaluza-Klein black hole looks like five dimensional black hole in the vicinity of horizon and four dimensional Minkowski...
Department of Fundamental Sciences, FIHS, (2007)
The higher dimensional spherical symmetric scalar field collapse problem is studied in the light of the critical behavior in black hole formation. To make the analysis tractable, the self similarity...
A Note on Separability of Field Equations in Myers-Perry Spacetimes (2007)
We study separability of scalar, vector and tensor fields in 5-dimensional Myers-Perry spacetimes with equal angular momenta. In these spacetimes, there exists enlarged symmetry, $U(2) \simeq SU(2)...
Kaluza-Klein braneworld cosmology with static internal dimensions (2007)
Kanno, Sugumi, Langlois, David, Sasaki, Misao, Soda, Jiro
We investigate the Kaluza-Klein braneworld cosmology from the point of view of observers on the brane. We first generalize the Shiromizu-Maeda-Sasaki (SMS) equations to higher dimensions. As an...
Satoh, Masaki, Kanno, Sugumi, Soda, Jiro
We study a mechanism to produce the circular polarization of primordial gravitational waves. The circular polarization is generated during the super-inflation driven by the Gauss-Bonnet term in the...
Renormalized Newtonian Cosmic Evolution with Primordial Non-Gaussianity (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...
Fate of Kaluza-Klein Black Holes: Evaporation or Excision? (2007)
Murata, Keiju, Soda, Jiro, Kanno, Sugumi
We study evaporation process of black strings which are typical examples of Kaluza-Klein black holes. Taking into account the backreaction of the Hawking radiation, we deduce the evolution equation...
Hawking Radiation from Squashed Kaluza-Klein Black Holes -- A Window to Extra Dimensions -- (2007)
We explore the obsevability of extra dimensions through 5-dimensional squashed Kaluza-Klein black holes residing in the Kaluza-Klein spacetime. With the expectation that the Hawking radiation...
Evaporating (2+1)-dimensional black strings (2007)
Murata, Keiju, Soda, Jiro, Kanno, Sugumi
We investigate (2+1)-dimensional black strings in the Kaluza-Klein spacetime. The system is classically stable as long as the horizon size is much larger than the size of the compact space....
Impact of Lorentz Violation on Cosmology (2006)
We discuss the impact of Lorentz violation on the cosmology. Firstly, we show that the Lorentz violation affects the dynamics of the chaotic inflationary model and gives rise to an interesting...
More on the Spectrum of Perturbations in String Gas Cosmology (2006)
Brandenberger, Robert H., Kanno, Sugumi, Soda, Jiro, Easson, Damien A., Khoury, Justin, Martineau, Patrick, ...
String gas cosmology is rewritten in the Einstein frame. In an effective theory in which a gas of closed strings is coupled to a dilaton gravity background without any potential for the dilaton, the...
Hawking Radiation from Rotating Black Holes and Gravitational Anomalies (2006)
We study the Hawking radiation from Rotating black holes from gravitational anomalies point of view. First, we show that the scalar field theory near the Kerr black hole horizon can be reduced to the...
Lorentz Violating Inflation (2006)
We explore the impact of Lorentz violation on the inflationary scenario. More precisely, we study the inflationary scenario in the scalar-vector-tensor theory where the vector is constrained to be...
Moduli Stabilization in String Gas Compactification (2005)
We investigate the moduli stabilization in string gas compactification. We first present a numerical evidence showing the stability of the radion and the dilaton. To understand this numerical result,...
Braneworld Cosmological Perturbation Theory at Low Energy (2005)
Homogeneous cosmology in the braneworld can be studied without solving bulk equations of motion explicitly. The reason is simply because the symmetry of the spacetime restricts possible corrections...
Black String Perturbations in RS1 Model (2005)
We present a general formalism for black string perturbations in Randall-Sundrum 1 model (RS1). First, we derive the master equation for the electric part of the Weyl tensor $E_{\mu\nu}$. Solving the...
Braneworld Flux Inflation (2005)
Kanno, Sugumi, Soda, Jiro, Wands, David
We propose a geometrical model of brane inflation where inflation is driven by the flux generated by opposing brane charges and terminated by the collision of the branes, with charge annihilation. We...
We present a general formalism for studying an inflationary scenario in the two-brane system. We explain the gradient expansion method and obtain the 4-dimensional effective action. Based on this...
On The Higher Codimension Braneworld (2004)
We study a codimension 2 braneworld in the Einstein-Gauss-Bonnet gravity. In the linear regime, we show the conventional Einstein gravity can be recovered on the brane. While, in the nonlinear...
On the Validity of a Factorizable Metric Ansatz in String Cosmology (2004)
To support the validity of a factorizable metric ansatz used in string cosmology, we investigate a toy problem in RSI model. For this purpose, we revise the gradient expansion method to conform to...
A Unified View of RS Braneworlds (2004)
There are various different descriptions of Randall-Sundrum (RS) braneworlds. Here we present a unified view of the braneworld based on the gradient expansion approach. In the case of the...
Quasi-Thick Codimension 2 Braneworld (2004)
We study a codimension 2 braneworld in the Einstein Gauss-Bonnet gravity. We carefully examine the structure of possible singularities in the system which characterize the braneworld through matching...
Gravitational Waves from Rotating Black Strings (2003)
In the Randall-Sundrum two-brane model (RS1), a Kerr black hole on the brane can be naturally identified with a section of rotating black string. To estimate Kaluza-Klein (KK) corrections on...
A Novel Approach to Braneworld (2003)
Evaluating Kaluza-Klein (KK) corrections is indispensable to test the braneworld scenario. In this report, we propose a novel symmetry approach to an effective 4-dimensional action with KK...
Effective Teukolsky Equation on the Brane (2003)
To estimate Kaluza-Klein (KK) corrections on gravitational waves emitted by perturbed rotating black strings, we give the effective Teukolsky equation on the brane which is separable equation and...
Radionic Non-uniform Stable Black Strings (2003)
Tamaki, Takashi, Kanno, Sugumi, Soda, Jiro
Non-uniform black strings in the two-brane system are investigated using the effective action approach. It is shown that the radion acts as a non-trivial hair of black strings. The stability of...
Inflationary Braneworld Driven By Bulk Scalar Field (2003)
We have developed a formalism to study an inflationary scenario driven by a bulk inflaton in the two-brane system. The 4-dimensional low energy effective action is obtained using the gradient...
Braneworld Kaluza-Klein Corrections in a Nutshell (2003)
Evaluating Kaluza-Klein (KK) corrections is indispensable to test the braneworld scenario. In this paper, we propose a novel symmetry approach to a 4-dimensional effective action with KK corrections...
Radionic Non-uniform Black Strings --short version-- (2003)
Tamaki, Takashi, Kanno, Sugumi, Soda, Jiro
Non-uniform black strings in the two-brane system are investigated using the effective action approach. It is shown that the radion acts as a non-trivial hair of black strings. The stability of...
Rotating Black String and Effective Teukolsky Equation in Braneworld (2003)
In the Randall-Sundrum two-brane model (RS1), a Kerr black hole on the brane can be naturally identified with a section of rotating black string. To estimate Kaluza-Klein (KK) corrections on...
Radionic Non-uniform Black Strings (2003)
Tamaki, Takashi, Kanno, Sugumi, Soda, Jiro
Non-uniform black strings in the two-brane system are investigated using the effective action approach. It is shown that the radion acts as a non-trivial hair of the black strings. From the brane...
We derive the low energy effective action for the dilatonic braneworld. In the case of the single-brane model, we find the effective theory is described by the Einstein-scalar theory coupled to the...
Non-linear Gravity on Branes and Effective Action (2003)
We develop the general formalism to study the low energy regime of the brane world. We apply our formalism to the single brane model where the AdS/CFT correspondence will take an important role. We...
Kanno, Sugumi, Sasaki, Misao, Soda, Jiro
We propose a cosmological braneworld scenario in which two branes collide and emerge as reborn branes with signs of tensions opposite to the original tensions of respective branes. In this scenario,...
Kanno, Sugumi, Sasaki, Misao, Soda, Jiro
We propose a cosmological braneworld scenario in which two branes collide and emerge as reborn branes whose tensions have signs opposite to the original tensions of the respective branes. In this...
Holographic View of Cosmological Perturbations (2002)
The cosmological perturbation theory is revisited from the holographic point of view. In the case of the single brane model, it turns out that the AdS/CFT correspondence plays an important role. In...
Braneworld Effective Action at Low Energies (2002)
The low energy effective theory for the Randall-Sundrum two-brane system is investigated with an emphasis on the role of the non-linear radion in the brane world. It is shown that the gravity on the...
Radion and Holographic Brane Gravity (2002)
The low energy effective theory for the Randall-Sundrum two brane system is investigated with an emphasis on the role of the non-linear radion in the brane world. The equations of motion in the bulk...
Cosmological Perturbations in Brane World - Brane view v.s. Bulk view - (2002)
First, we will study the cosmological perturbations from the brane point of view. It turns out that two types of the extra data are necessary to know the evolution of the system. To fix these data,...
Brane World Effective Action at Low Energies and AdS/CFT Correspondence (2002)
A low energy iteration scheme to study nonlinear gravity in the brane world is developed. As a result, we obtain the brane world effective action at low energies. The relation between the geometrical...
Gravitational Waves in Brane World -A Midi-superspace Approach- (2002)
It is important to reveal the brane-bulk correspondence for understanding the brane world cosmology. When gravitational waves exist in the bulk, however, it is difficult to make the analysis of the...
Recently, branes in supergravity have become an indispensable tool even for traditional relativists. The purpose of this manuscript is to provide a pedagogical account of the brane technology so that...
Bulk Gravitational Field and Cosmological Perturbations on the Brane (2001)
We investigate the effect of the bulk gravitational field on the cosmological perturbations on a brane embedded in the 5D Anti-de Sitter (AdS) spacetime. The effective 4D Einstein equations for the...
Thick Brane Worlds and Their Stability (2001)
Kobayashi, Shinpei, Koyama, Kazuya, Soda, Jiro
Three types of thick branes, i.e., Poincar\'{e}, de Sitter and Anti-de Sitter brane are considered. They are realized as the non-singular solutions of the Einstein equations with the non-trivial...
Strongly Coupled CFT in FRW Universe from AdS/CFT Correspondence (2001)
We develop a formalism to calculate the effective action of the strongly coupled conformal field theory (CFT) in curved spacetime. The effective action of the CFT is obtained from AdS/CFT...
Black Hole in Higher Curvature Gravity and AdS/CFT Correspondence (2000)
The classical central charge for the higher curvature gravity in 3-dimensions is calculated using the Legendre transformation method. The statistical entropy of BTZ black hole is derived by the...
Quantum Fluctuations of Bulk Inflaton in Inflationary Brane World (2000)
Kobayashi, Shinpei, Koyama, Kazuya, Soda, Jiro
The inflationary scenario for the brane world driven by the bulk inflaton is proposed. The quantum fluctuations of the inflaton is calculated and compared to those of the conventional 4-dimensional...
Black holes and a scalar field in an expanding universe (2000)
We consider a model of an inhomogeneous universe including a massless scalar field, where the inhomogeneity is assumed to consist of many black holes. This model can be constructed by following...
Evolution of Cosmological Perturbations in the Brane World (2000)
The evolution of the cosmological perturbations is studied in the context of the Randall-Sundrum brane world scenario, in which our universe is realized on a three-brane in the five dimensional...
Birth of the Brane World (2000)
Birth of the brane world is studied using the Hamiltonian approach. It is shown that an inflating brane world can be created from nothing. The wave function of the universe obtained from the Wheeler...
Creation of an Open Universe from Valley Bounce (2000)
Koyama, Kazuya, Maeda, Kayoko, Soda, Jiro
It appears difficult to construct a simple model for an open universe based on the one bubble inflationary scenario. The reason is that one needs a large mass to avoid the tunneling via the Hawking...
BTZ Black Hole Entropy in Higher Curvature Gravity (2000)
For the BTZ black hole in the Einstein gravity, a statistical entropy has been calculated. It is equal to the Bekenstein-Hawking entropy. In this article, its statistical entropy in the higer...
An Open Universe from Valley Bounce (1999)
Koyama, Kazuya, Maeda, Kayoko, Soda, Jiro
It appears difficult to construct a simple model for an open universe based on the one bubble inflationary scenario. The reason is that one needs a large mass to avoid the tunneling via the Hawking...
Statistical Entropy of BTZ Black Hole in Higher Curvature Gravity (1999)
For the BTZ black hole in the Einstein gravity, a statistical entropy has been calculated to be equal to the Bekenstein-Hawking entropy. In this paper, the statistical entropy of the BTZ black hole...
Structure Formation in Non-singular Higher Curvature Cosmology (1999)
We propose novel structure formation scenarios based on a non-singular higher curvature cosmological model. The model is motivated by the $R^2$ coupling of a scalar field appearing in the string...
Evolution of Fluctuations during Graceful Exit in String Cosmology (1999)
We study the evolution of fluctuations in a universe dominated by a scalar field coupled to the Gauss-Bonnet term. During the graceful exit, we found non-negligible enhancements of both curvature...
Constraints on a non-gaussian ($\chi_m^2$) CDM model (1999)
Koyama, Kazuya, Soda, Jiro, Taruya, Atsushi
We consider constraints on the structure formation model based on non-Gaussian fluctuations generated during inflation, which have $\chi_m^2$ distributions. Using three data sets, the abundance of...
Perturbative analysis of non-singular cosmological model (1999)
Kawai, Shinsuke, Sakagami, Masa-aki, Soda, Jiro
A stability analysis is made for a non-singular pre-big-bang like cosmological model based on 1-loop corrected string effective action. Its homogeneous and isotropic solution realizes non-singular...
Baryon Isocurvature Perturbation in the Affleck-Dine Baryogenesis mechanism (1998)
We propose a primeval baryon isocurvature model in the context of the Affleck-Dine (AD) baryogenesis mechanism. Quantum fluctuations of the AD field during inflation produce fluctuations in the...
Nonsingular Bianchi type I cosmological solutions from 1-loop superstring effective action (1998)
Non-singular Bianchi type I solutions are found from the effective action with a superstring-motivated Gauss-Bonnet term. These anisotropic non-singular solutions evolve from the asymptotic Minkowski...
Novel Instability in Superstring Cosmology (1998)
Soda, Jiro, Sakagami, Masa-aki, Kawai, Shinsuke
As a most promising candidate for quantum theory of the gravity, the superstring theory has attracted many researchers including cosmologists. It is expected that the cosmological initial singularity...
Instability of 1-loop superstring cosmology (1998)
Kawai, Shinsuke, Sakagami, Masa-aki, Soda, Jiro
A stability analysis is made in the context of the previously discovered non-singular cosmological solution from 1-loop corrected superstring effective action. We found that this solution has an...
On the Canonical Formalism for a Higher-Curvature Gravity (1998)
Ezawa, Yasuo, Kiminami, Masahiko, Kajihara, Masahiro, Soda, Jiro, Yano, Tadasi
Following the method of Buchbinder and Lyahovich, we carry out a canonical formalism for a higher-curvature gravity in which the Lagrangian density ${\cal L}$ is given in terms of a function of the...
Soda, Jiro, Hirata, Kouichirou
The higher dimensional spherical symmetric scalar field collapse problem is studied in the light of the critical behavior in black hole formation. To make the analysis tractable, the self similarity...
Critical Behavior in the Brans-Dicke Theory of Gravitation (1996)
The collapse of a massless scalar field in the Brans-Dicke theory of gravitation is studied in the analysis of both analytical solution and numerical one. By conformally transforming the Roberts's...
Comment on Entropy in Two-dimensional Dilaton Gravity (1996)
Hirata, Kouichirou, Fujiwara, Yoshi, Soda, Jiro
The thermodynamic second law in the evaporating black hole space-time is examined in the context of two-dimensional dilaton black hole. The dynamical evolution of entropy is investigated by using the...
Wavelet Analysis of One-Dimensional Cosmological Density Fluctuations (1995)
Wavelet analysis is proposed as a new tool for studying the large-scale structure formation of the universe. To reveal its usefulness, the wavelet decomposition of one-dimensional cosmological...
Hamilton-Jacobi Equation for Brans-Dicke Theory and Its Long-wavelength Solution (1995)
Soda, Jiro, Ishihara, Hideki, Iguchi, Osamu
Hamilton-Jacobi equation for Brans-Dicke theory is solved by using a long-wavelength approximation. We examine the non-linear evolution of the inhomogeneities in the dust fluid case and the...