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Takuya Maki

Publications and source records attributed to Takuya Maki.

At least 19 recordsLinked to original sources
arXiv2024

Isothermal spheres from grand partition functions in nonextensive statistical mechanics

We analytically study isothermal spheres in the light of nonextensive statistical mechanics. The equations for the isothermal spheres are derived from the grand partition function of the gravitating particle system in the Tsallis statistical mechanics. The effect of nonextensive statistics appears in relatively dense state, which appears at the center of the isothermal sphere. The stability of the isothermal sphere in the general relativistic system is found to be sensitive to the parameter q in the Tsallis statistics.

gr-qc↗
arXiv2020

Vacuum polarization around a three-dimensional black hole

We calculate the Euclidean propagator for a conformally coupled massless scalar field in the background of the three-dimensional black hole. The expectation value $\langleφ^2\rangle$ in the Hartle-Hawking state is obtained in the spacetime.

gr-qc↗
arXiv2019

High-Energy Scattering by Extreme Dilaton Black Holes

We investigate the high and low energy scattering of charged scalar waves from an extreme dilaton black hole (DBH). The analyses here correspond to forward scattering processes of two charged scalar particles with dilaton coupling under a certain extreme condition. We calculate the scattering amplitude and compare it with the known results obtained by other methods. We also discuss the case of incoming wave with a general charge and dilaton coupling.

hep-th↗
arXiv2019

Vacuum polarization near asymptotically anti-de Sitter black holes in odd dimensions

Recently, Bañados, Teitelboim and Zanelli obtained spherically symmetric black hole solutions in a particular class of Einstein--Lovelock gravity. We derive the propagator in an exact form for a conformal scalar field in the asymptotically anti-de Sitter black hole spacetime so as to study the quantum effects of the scalar fields. We treat the cases in odd dimensions in this paper. We calculate the vacuum expectation value of $\langleφ^2\rangle$ and show its dependence on the radial coordinate for the five-dimensional case as an example.

gr-qc↗
arXiv2016

GR-GSG Hybrid Gravity

We propose a model of gravity in which a General Relativity metric tensor and an effective metric generated from a single scalar formulated in Geometric Scalar Gravity are mixed. We show that the model yields the exact Schwarzschild solution, along with accelerating behavior of scale factors in cosmological solutions.

gr-qc↗
arXiv2015

More on quantum kinks in gauge theories on $R^2 \otimes S^1$

Quantum kinks in gauge theories on $R^2\otimes S^1$ space-time are studied. To obtain the, explicit profile of the kinks, we calculated effective actions including derivative corrections for vacuum gauge fields on $S^1$ at zero, and finite temperature up to one-loop level. It is found that there are soliton solutions in scalar QED. We also find that the derivative correction tends to make the vacuum unstable in $SU(2)$ Yang-Mills theory.

math-ph↗
arXiv2014

Spontaneous Compactification of Bimetric Theory

We propose a model of bimetric gravity in which the mixing of metrics naturally gives a mass to a graviton by the compactification with flux of two gauge fields in extra dimensions. We assume that each metric in the solution for the background geometry describes the four-dimensional Minkowski spacetime with an $S^2$ extra space, though the two radii of $S^2$ for two metrics take different values in general. The solution is derived by the effective potential method in the presence of the magnetic fluxes on the extra spheres. We find that the a massive graviton is governed by the Fierz-Pauli Lagrangian in the weak field limit and one massless graviton left in four dimensions.

hep-th↗
arXiv2014

Magnetic Moment of Electrons near Cosmic Strings

We study the effect of background geometry generated by a thin cosmic string on the anomalous magnetic moment of the electron. We find that the magnitude of the quantum correction to the magnetic moment depends on the distance from the cosmic string as well as on the deficit angle.

hep-th↗
arXiv2012

On the cosmology of Weyl's gauge invariant gravity

Recently the vector inflation has been proposed as the alternative to inflationary models based on scalar bosons and quintessence scalar fields. In the vector inflationary model, the vector field non-minimally couples to gravity. We should, however, inquire if there exists a relevant fundamental theory which supports the inflationary scenario. We investigate the possibility that Weyl's gauge gravity theory could be such a fundamental theory. That is the reason why the Weyl's gauge invariant vector and scalar fields are naturally introduced. After rescaling the Weyl's gauge invariant Lagrangian to the Einstein frame, we find that in four dimensions the Lagrangian is equivalent to Einstein-Proca theory and does not have the vector field non-minimally coupled to gravity, but has the scalar boson with a polynomial potential which leads to the spontaneously symmetry breakdown.

gr-qc↗
arXiv2011

Flux vacua in Dirac-Born-Infeld type Einstein-Maxwell theory

We study compactification of extra dimensions in a theory of Dirac-Born-Infeld (DBI) type gravity. We investigate the solution for Minkowski spacetime with an $S^{2}$ extra space. The solution is derived by the effective potential method in the presence of the magnetic flux on the extra sphere. We find that, in a certain model, the radius of the extra space has a minimum value independent of the higher-dimensional Newton constant in weak-field limit.

gr-qc↗
arXiv2011

Flux vacua in DBI type Einstein-Maxwell theory

We study compactification of extra dimensions in a theory of Dirac-Born-Infeld (DBI) type gravity. We investigate the solution for Minkowski spacetime with an $S^2$ extra space as well as that for de Sitter spacetime ($S^4$) with an $S^2$ extra space. They are derived by the effective potential method in the presence of the magnetic flux on the extra sphere. We also consider the higher dimensional generalization of the solutions. We find that, in a certain model, the radius of the extra space has a minimum value independent of the higher-dimensional Newton constant in weak-field limit.

gr-qc↗