arXiv subjects

Yasusada Nambu

Publications and source records attributed to Yasusada Nambu.

79 records · Page 5Linked to original sources

arXiv1998

Solutions of gauge invariant cosmological perturbations in long-wavelength limit

We investigate gauge invariant cosmological perturbations in a spatially flat Friedman-Robertson-Walker universe with scalar fields. It is well known that the evolution equation for the gauge invariant quantities has exact solutions in the long-wavelength limit. We find that these gauge invariant solutions can be obtained by differentiating the background solution with respect to parameters contained in the background system. This method is very useful when we analyze the long-wavelength behavior of cosmological perturbation with multiple scalar fields.

gr-qc↗

arXiv1998

Renormalization group equations and integrability in Hamiltonian systems

We investigate Hamiltonian systems with two degrees of freedom by using renormalization group method. We show that the original Hamiltonian systems and the renormalization group equations are integrable if the renormalization group equations are Hamiltonian systems up to the second leading order of a small parameter.

chao-dyn↗

arXiv1996

Evolution of Cosmological Perturbation in Reheating Phase of the Universe

The evolution of the cosmological perturbation during the oscillatory stage of the scalar field is investigated. For the power law potential of the inflaton field, the evolution equation of the Mukhanov's gauge invariant variable is reduced to the Mathieu equation and the density perturbation grows by the parametric resonance.

gr-qc↗

arXiv1995

Application of gradient expansion to non-linear gravitational wave in plane-symmetric universe

As an application of Gradient Expansion (long-wavelength) approximation, we studied the inhomogeneous universe including the gravitational wave(GW). For a plane-symmetric cosmological model, we could implement the 2nd order expansion and analyze the purely non-linear perturbation of GW. The result indicates that the non-linear effect plays an important role in anisotropic stage of the universe. We also confirm that the perturbation from the linear source term in gradient expansion is consistent with the result of linear perturbation.

gr-qc↗

arXiv1994

Application of Gradient Expansion to Inflationary Universe

Using the long wave perturbation scheme(gradient expansion), the effect of inhomogeneity on the inflationary phase is investigated. We solved the perturbation equation of which source term comes from inhomogeneity of a scalar field and a seed metric. The result indicates that sub-horizon scale inhomogeneity strongly affects the onset of inflation.

astro-ph↗

arXiv1993

Local Structure of Numerically Generated Worm Hole Spacetime

We investigate the evolution of the apparent horizons in a numerically gererated worm hole spacetime. The behavior of the apparent horizons is affected by the dynamics of the matter field. By using the local mass of the system, we interpret the evolution of the worm hole structure. Figures are available by mail to author.

gr-qc↗

arXiv1993

Fate of Inhomogeneity in Schwarzschild-deSitter Space-time

We investigate the global structure of the space time with a spherically symmetric inhomogeneity using a metric junction, and classify all possible types. We found that a motion with a negative gravitational mass is possible although the energy condition of the matter is not violated. Using the result, formation of black hole and worm hole during the inflationary era is discussed.

gr-qc↗