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Masashi Kuniyasu

Publications and source records attributed to Masashi Kuniyasu.

8 recordsLinked to original sources
arXiv2021

Quantum fluctuation of stress tensor in a higher-derivative scalar field theory around a cosmic string

We calculate the vacuum fluctuation of the stress tensor of a higher-derivative theory around a thin cosmic string. To this end, we adopt the method to obtain the stress tensor from the effective action developed by Gibbons et al. By their method, the quantum stress tensor of higher-derivative scalar theories without self-interaction is expressed as a simple sum of quantum stress tensors of free massive scalar fields. Unlike the vacuum expectation value of the scalar field squared obtained in the similar model, there appears no reduction of the values near the conical singularity.

hep-th↗
arXiv2021

Discrete heat kernel, UV modified Green's function, and higher derivative theories

We perform the UV deformation of the Green's function in free scalar field theory using a discrete heat kernel method. It is found that the simplest UV deformation based on the discretized diffusion equation leads to the well-known Pauli-Villars effective Lagrangian. Furthermore, by extending assumptions on the discretized equation, we find that the general higher derivative theory is derived from the present UV deformation. In some specific cases, we also calculate the vacuum expectation values of the scalar field squared in nontrivial background spaces and examine their dependence on the UV cutoff constant.

hep-th↗
arXiv2020

Accelerating cosmologies in an integrable model with noncommutative minisuperspace variables

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.

gr-qc↗
arXiv2020

Equivalent Hamiltonian approach to quantum cosmology of integrable models

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.

gr-qc↗
arXiv2018

Integrable higher-dimensional cosmology with separable variables in an Einstein-dilaton-antisymmetric field theory

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.

hep-th↗
arXiv2015

New Solutions of the $2+1$ Dimensional Einstein Gravity Coupled to Maxwell Power type Non Linear Electric field with Dilaton field

New solutions are derived in the $2+1$ gravity which is coupled to $|{\cal F}|^k$ type non-linear electric field in Maxwell Power theory with dilaton field. We obtain consistent solutions in general $k$ case. We also investigate the behavior of the metric function with the space-time singularity. Then, we found some black hole solutions when the space-time has a singular point at $r=0$. Addition, we derive the Brown-York mass when the space-time represents black hole.

gr-qc↗
arXiv2014

A New 2+1 Dimensional Einstein Gravity Solution Coupled to Born-Infeld Electromagnetic Theory without Cosmological Constan

A new solution of the Einstein-Born-Infeld theory in 2+1 space-time is derived. A new solution has no horizon there are two singularity. This space-time has two singular points, however, one of the point at the origin is not in the physical region. We also investigate the energycondition. Then, weak energy condition is satisfied. However, causal energy condition is violated.

gr-qc↗