arXiv subjects
Publications and source records attributed to Kiyoshi Shiraishi.
We evaluate the quantum expectation values in non-simply connected spaces by using UV improved Green's functions proposed by Padmanabhan, Abel, and Siegel. It is found that the results from these three types of Green's functions behave similarly under changes of scales, but have minute differences. Prospects in further applications are briefly discussed.
We study classical and quantum noncommutative cosmology with a Liouville-type scalar degree of freedom. The noncommutativity is imposed on the minisuperspace variables through a deformation of the Poisson algebra. In this paper, we investigate the effects of noncommutativity of minisuperspace variables on the accelerating behavior of the cosmic scale factor. The probability distribution in noncommutative quantum cosmology is also studied and we propose a novel candidate for interpretation of the probability distribution in terms of noncommutative arguments.
The energy density of a conformally invariant scalar field around a cosmic string is estimated by the WKB method. This approach reproduces the precise value obtained by the other authors using the exact mode-sum method or the method of mirror images. The approximation is also in good agreement with the exact result in the three-dimensional case. We also evaluate the energy density of a conformally invariant scalar field around a global monopole by the same way and find the known result again.
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.
We propose an approach to quantum cosmology of integrable models. To analyze the models with two dynamical variables, we introduce equivalent Hamiltonians in reduced phase spaces, which are obtained with the aid of the Faddeev--Jackiw method. Quantum dynamics of the models can be studied by using the equivalent Hamiltonians with various techniques.
The authors study the quantum effect of self-interacting fields in the classical background of conical space, i.e. around a cosmic string with infinitesimal width. The renormalized value of $\langleϕ^2\rangle$ and energy-momentum tensor in the presence of cosmic strings are calculated in the self-interacting scalar field theory. The amount of condensation is also estimated in the case of the Dirac Lagrangian with the four-fermion interaction. The physical implications of the above analyses are discussed.
If two dimensions of six-dimensional space-time are compactified, a topological configuration of Yang-Mills gauge field appears as a cosmic string in four dimensions, whose thickness is of the same order as the size of the compact space. We consider scattering of low-energy fermions by this object.
We present a gravitational action with a modified higher order term of a combination of scalar curvature and Lagrangian density of a scalar field. This type of models has been considered first by Cruz-Dombriz et al. The classical and quantum cosmologies governed by the modified action are studied. Models described by a positive-definite action and a pure arbitrary-powered scalar curvature action without the standard Einstein-Hilbert term are also investigated. We show some particular cases in which exact solutions can be obtained.
We present a new class of the black hole solutions of Einstein-Maxwell-Yang-Mills theory. These solutions have both U(1) charge and Yang-Mills hair. We also investigate the thermodynamic properties.
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.
The discrete Gel'fand--Yaglom theorem was studied several years ago. In the present paper, we generalize the discrete Gel'fand--Yaglom method to obtain the determinants of mass matrices which appear current works in particle physics, such as dimensional deconstruction and clockwork theory. Using the results, we show the expressions for vacuum energies in such various models.
We present time-dependent analytic solutions to the Einstein equations coupled with a dilaton (scalar) field. The background geometry for the solutions is a product of an N-dimensional spherically symmetric space and a d-dimensional flat space. We discuss the global properties of the spacetime.
A solution of the vortex type is given in a six-dimensional $SU(2)\times U(1)$ pure gauge theory coupled to Einstein gravity in a compactified background geometry. We construct the solution of an effective abelian Higgs model in terms of dimensional reduction. The solution, however, has a peculiarity in its physically relevant quantity, a deficit angle, which is given as a function of the ratio of the gauge couplings of $SU(2)$ and $U(1)$. The size of the extra space (sphere) is shown to vary with the distance from the axis of the "string".
Adopting a simple ansatz, we find exact solutions to the Einstein-Maxwell-dilaton equations, which stand for the multi-black hole configuration with maximal charge in a cosmological metric and dilaton field background driven by a cosmological term.
The classical and the quantum scattering of two maximally-charged dilaton black holes which have low velocities are studied. We find a critical value for the dilaton coupling, $a^2=1/3$. For $a^2>1/3$, two black holes are always scattered away and never coalesce together, regardless of the value of the impact parameter.
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.
We study vortex solutions in the Born-Infeld theory coupled with a complex scalar field. We show that for a specific form of the "Higgs" potential the vortex satisfies a set of Bogomol'nyi-type equations. Another model, with nonlinear interaction between gauge and Higgs fields, is also considered. We show how it is derived from a supersymmetric extension of the Born-Infeld theory with a minimally coupled complex scalar field.
We consider a $D$-dimensional cosmological model with a dilaton field and two $(D-d-1)$-form field strengths which have nonvanishing fluxes in extra dimensions. Exact solutions for the model with a certain set of couplings are obtained by separation of three variables. Some of the solutions describe accelerating expansion of the $d$-dimensional space. Quantum cosmological aspects of the model are also briefly mentioned.