arXiv subjects

Jiro Soda

Publications and source records attributed to Jiro Soda.

188 records · Page 11Linked to original sources

arXiv1998

Novel Instability in Superstring Cosmology

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 is avoided within the context of the superstring theory. Indeed, Antoniadis et. al. found an interesting example of the non-singular cosmological solutions by considering the string one-loop correction. Here, we will discuss the stability of this model and find a new kind of instability in the graviton modes. We also argue this instability will persist even in the non-perturbative regime. The instability we have found might provide a mechanism to produce the primodial black holes.

gr-qc↗

arXiv1998

Instability of 1-loop superstring cosmology

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 instability in graviton mode, which is shown to have a close relation to the avoidance of initial singularity via energy condition. We also estimate the condition for the breakdown of the background solution due to the overdominance of the graviton.

gr-qc↗

arXiv1998

On the Canonical Formalism for a Higher-Curvature Gravity

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 salar curvature $R$ as ${\cal L}=\sqrt{-\det g_{μν}}f(R)$. The local Hamiltonian is obtained by a canonical transformation which interchanges a pair of the generalized coordinate and its canonical momentum coming from the higher derivative of the metric.

gr-qc↗

arXiv1996

Higher Dimensional Self-similar Spherical Symmetric Scalar Field Collapse and Critical Phenomena in Black Hole Formation

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 is also imposed. By giving a new view to the self-similar scalar field collapse problem, we give the general formula for the critical exponents in higher dimensions. In the process, the explanation of the universality of the critical phenomena is given within the self-similar context.

gr-qc↗

arXiv1996

Critical Behavior in the Brans-Dicke Theory of Gravitation

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 solution into the Brans-Dicke frame, we find for $ω> -3/2$ that a continuous self-similarity continues and that the critical exponent does depend on $ω$. By conformally transforming the Choptuik's solution into the Brans-Dicke frame, we find for $ω> -3/2$ that at the critical solution shows discrete self-similarity, however, the critical exponent depends strongly on $ω$ while the echoing parameter weakly on it.

gr-qc↗

arXiv1996

Comment on Entropy in Two-dimensional Dilaton Gravity

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 analytical perturbation method and the numerical method. It is shown that the thermodynamic second law holds in the vicinity of infalling shell %analytically and in the region far from the infalling shell %numerically in the case of semi-classical CGHS model. The analysis of the general models is also presented and its implication is discussed.

gr-qc↗

arXiv1995

Wavelet Analysis of One-Dimensional Cosmological Density Fluctuations

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 density fluctuations is performed. In contrast with the Fourier analysis, the wavelet analysis has advantage of its ability to keep the information for location of local density peaks in addition to that for their scales. The wavelet decomposition of evolving density fluctuations with various initial conditions is examined. By comparing the wavelet analysis with the usual Fourier analysis, we conclude that the wavelet analysis is promising as the data analysis method for the Sloan Digital Sky Survey and COBE.

astro-ph↗

arXiv1995

Hamilton-Jacobi Equation for Brans-Dicke Theory and Its Long-wavelength Solution

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 cosmological constant case. In the case of dust fluid, it turns out that the inhomogeneities of space-time grow. In the case of cosmological constant, the inhomogeneities decay, which is consistent with the cosmic no hair conjecture. The inhomogeneities of the density perturbation and the gravitational constant behave similarly with that of space-time.

gr-qc↗