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Nahomi Kan

Publications and source records attributed to Nahomi Kan.

At least 37 records · Page 2Linked to original sources
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↗
arXiv2019

Classical and quantum cosmology of $K$-essentially modified $R^2$ and pure $R^p$ gravity

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.

gr-qc↗
arXiv2019

Deconstructing the Gel'fand--Yaglom method and vacuum energy from a theory space

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.

math-ph↗
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↗
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

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↗
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

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↗
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

A Model of BPS Black Holes in a Discrete Space

We examine a model of BPS black holes lying on a discrete extra space. The geometry is obtained from the discretization of the harmonic equation. We study the scattering amplitudes of two types of scalar fields, which correspond to fields in a bulk and on a brane. We conclude that the two types of scattering can be distinguished in the region of large transfer momentum.

gr-qc↗
arXiv2013

Simple Models in Supersymmetric Quantum Mechanics on a Graph

We study some sorts of dimensionally-deconstructed models for supersymmetric (Euclidean) quantum mechanics, or zero-dimensional field theory. In these models, we assign bosonic and fermionic variables to vertices and edges of a graph. We investigate a discrete version for the Gaussian model and the Wess-Zumino-type model on a graph. The topological index as a multiple integral is discussed on these models. In addition, we propose simple examples for supersymmetric extensions of the Lee-Wick model and the Galileon model. A model with two supersymmetries is also provided and generalization to `local' supersymmtric models is examined.

math-ph↗
arXiv2013

Critical Higher Order Gravities in Higher Dimensions

We show that the higher order gravity model proposed by Meissner and Olechowski has a graviton mode, a massive spin-two excitation and no scalar mode in a maximally symmetric spacetime; therefore, by choosing the coefficients, we can construct a Lagrangian for `critical gravity' from higher order terms of curvatures in higher dimensions. We also give a comment on construction of the theory with multi-criticality in higher order gravities.

hep-th↗