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Kiyoshi Shiraishi

Publications and source records attributed to Kiyoshi Shiraishi.

At least 55 records · Page 3Linked to original sources
arXiv2018

Condensation of Yang-Mills field at High Temperature in the Presence of Fermions

The possible condensation of the time-component of Yang-Mills field at finite temperature is discussed in the presence of Dirac fermions. We show that the condensation forms regardless of the number of fundamental and adjoint fermion species coupled to the Yang-Mills field. The effect of finite density of fermions is also investigated and it is shown that the magnitude of the condensation is also independent of the densities.

hep-th↗
arXiv2018

An ostentatious model of cosmological scalar-tensor theory

We consider a novel model of gravity with a scalar field described by the Lagrangian with higher order derivative terms in a cosmological context. The model has the same solution for the homogeneous and isotropic universe as in the model with the Einstein gravity, notwithstanding the additional higher order terms. A possible modification scenario is briefly discussed lastly.

gr-qc↗
arXiv2018

Magnetic monopoles in multi-vector boson theories

A classical solution for a magnetic monopole is found in a specific multi-vector boson theory. We consider the model whose $[SU(2)]^{N+1}$ gauge group is broken by sigma-model fields (à la dimensional deconstruction) and further spontaneously broken by an adjoint scalar (à la triplet Higgs mechanism). In this multi-vector boson theory, we find the solution for the monopole whose mass is $M_N\sim\frac{4πv}{g}\sqrt{N+1}$, where $g$ is the common gauge coupling constant and $v$ is the vacuum expectation value of the triplet Higgs field, by using a variational method with the simplest set of test functions.

hep-th↗
arXiv2018

Euclidean wormhole solutions of Einstein-Yang-Mills theory in diverse dimensions

We solve the Euclidean Einstein equations with non-Abelian gauge fields of sufficiently large symmetry in various dimensions. In higher-dimensional spaces, we find the solutions which are similar to so-called scalar wormholes. In four-dimensional space-time, we find singular wormhole solutions with infinite Euclidean action. Wormhole solutions in the three-dimensional Einstein-Yang-Mills theory with a Chern-Simons term are also constructed.

gr-qc↗
arXiv2018

Analytical Study of Charged Boson Stars with Large Scalar Self-couplings

We give good approximate analytic solutions for spherical charged boson stars in the large scalar-self-coupling limit in general relativity. We show that if the charge $e$ and mass $m$ of the scalar field nearly satisfy the critical relation $e^2\approx Gm^2$ (where $G$ is the Newton constant), our analytic expressions for stable solutions agree well with the numerical solutions.

gr-qc↗
arXiv2018

Vacuum energy for Yang-Mills fields in $R^d\times S^1$: One-loop, two-loop, and beyond

The vacuum energy is calculated for Yang-Mills (YM) system defined in $D$ dimensional space-time of $S^1\times R^d$ ($D=d+1$), where the possibility of the YM fields to acquire the vacuum expectation values on $S^1$ is taken into account. The vacuum energy has already been obtained to the order of one-loop in many people. Here we calculate the vacuum energy in $D$ dimensions to two-loop order. With an intention to reach higher loops, an approximation method is proposed, which is especially effective in higher dimensions. By this method, we can treat the higher-loop contributions of YM interactions as easily as we treat one-loop effect. As a check, we show reproduction of the two-loop contribution ($D$-dependence of the coefficient as well as the functional form) when the coupling constant is small. This approximation method is useful not only for the Kaluza-Klein theories but also for the finite temperature-density system (as a quark-gluon plasma).

hep-th↗
arXiv2018

Degenerate Fermions and Wilson Loop in $1+1$ Dimensions

We investigate the effect of finite fermion density on symmetry breaking by Wilson loops in $(1+1)$ dimensions. We find the breaking and restoration of symmetry at finite density in the models with $SU(2)$ and $SU(3)$ gauge symmetries, in the presence of the adjoint fermions. The transition can occur at a finite density of fermions, regardless of the periodic or antiperiodic boundary condition of the fermion field; this is in contrast to the finite-temperature ease examined by Ho and Hosotani (Nucl. Phys. B345 (1990) 445) where the boundary condition of fractional twist is essential to the occurrence of the phase transition.

hep-th↗
arXiv2017

Phase Transition and String Formation in Six-Dimensional Gauge Theory

We consider an SU(2) gauge theory in six-dimensions. We show that there exists non-trivial structure of gauge vacua in compactified background M4xS2. In this circumstances, there can exist a cosmic string, whose solution is recently constructed by the present authors. We consider the stage of the formation of the strings, i.e., the phase transition of the gauge configuration on the sphere in the `hot' early universe. We find that if SU(2)-doublet fermions are the dominant component of the radiation at high temperatures, the phase transition successively occurs after the spontaneous-compactification transition. Otherwise, non-trivial vacuum with `monopole' configuration of the SU(2) gauge field never appears globally and strings must be formed at the same time as the extra space is compactified.

hep-th↗
arXiv2017

A Newtonian Analysis of Multi-scalar Boson Stars with Large Self-couplings

We study solutions for boson stars in the multi-scalar field theory with global symmetry $[U(1)]^N$. The properties of the boson stars are investigated by the Newtonian approximation with the large coupling limit. Our purpose is to study the models bringing about exotic mass distributions which explain flat rotation curves of galaxies. We propose plausible models in which coupling matrices are associated with various graphs in graph theory.

hep-th↗
arXiv2016

Analytical Approximation for Newtonian Boson Stars in Four and Five Dimensions -- A Poor Person's Approach to Rotating Boson Stars

In this paper, we study rotating boson stars in the large coupling limit as well as in the Newtonian limit. We investigate the equilibrium solutions in four and five dimensions by adopting some analytical approximations. We show that the relations among the radius, angular momentum, Newtonian energy and quadrupole moment (for the four-dimensional solution) of the boson star can be qualitatively realized for the minimal number of boson star parameters.

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

Global strings in five-dimensional supergravity

We show the existence of solitonic solutions of five-dimensional supergravity, which can be interpreted as global cosmic strings in our universe. They possess the same mathematical structure as the stringy cosmic strings studied by Greene, Shapere, Vafa and Yau, while the size of the extra space and the value of the extra-space component of the gauge field vary from place to place around the string in our model. We also show that supersymmetry is partially broken in the presence of the global strings.

hep-th↗
arXiv2015

Spinning a charged dilaton black hole

A charged dilaton black hole which possesses infinitesimal angular momentum is studied. We find that the gyromagnetic ratio of the dilaton black hole depends not only on the parameter which appears in the interaction between the dilaton and the electric field but also nonlinearly on the ratio of the charge to the mass of the black hole. The moment of inertia for the charged dilaton hole in the limit of infinitesimal angular momentum is also calculated.

gr-qc↗
arXiv2015

Generic Scalar Potentials in Geometric Scalar Gravity

We discuss a generic form of the scalar potential appearing in the geometric scalar theory of gravity. We find the conditions on the potential by considering weak and strong gravity. The modified black hole solutions are obtained for generic potentials and the inverse problems on a black hole and on a spherical body (`pseudo-gravastar') are investigated.

gr-qc↗