arXiv subjects
Publications and source records attributed to Koichiro Kobayashi.
By projecting the partition function on the "color"-singlet state, we investigate the Hosotani mechanism in the fermion-gauge boson plasma. The present toy-model analysis of the one-loop effective potential at finite temperature shows that the critical temperature of gauge symmetry breaking increases at higher temperature in the smaller volume.
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.
The effects of the axion field have been widely studied in theoretical physics, particularly in particle physics. Considering the phase synchronization and the mean free path of the axion, the bulk of the phase coherent superconductor is regarded as the weak link region of the Josephson junction.It is expected that the axion mass influences the London penetration depth.There is a slight possibility of detecting this effect because the effect becomes more significant in superconductor with a low carrier density $n_s$.The differences due to the choice of axion model and the axion mass are discussed.
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.
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.
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.
Hosotani mechanism in higher-dimensional Lee-Wick theory is investigated. The symmetry breaking mechanism proposed by Hosotani is studied at one-loop level through a toy model in this theory. We find that the phase diagram of symmetry and masses of fields are modified from the original one if masses of Lee-Wick particles are in the same order of the inverse of the compactification scale.
We construct the higher order terms of curvatures in Lagrangians of the scale factor for the Friedmann-Lemaitre-Robertson-Walker universe, which are linear in the second derivative of the scale factor with respect to cosmic time. It is shown that they are composed from the Lovelock tensors at the first step; iterative construction yields arbitrarily high order terms. The relation to the former work on higher order gravity is discussed. Despite the absence of scalar degrees of freedom in cosmological models which come from our Lagrangian, it is shown that an inflationary behavior of the scale factor can be found. The application to the thick brane solutions is also studied.
The Nambu-Jona-Lasinio model with the mass matrix which appears in a deconstruction model is investigated. We consider two models. In Model A, a mass matrix belonging to a type used in dimensional deconstruction is introduced. In Model B, the four-fermion interaction has a structure of the matrix of the type of dimensional deconstruction. In these models, we find that generation of a dynamical fermion mass spectrum occurs in a strong coupling case.
The equation of motion for a point particle in the background field of double field theory is considered. We find that the motion is described by a geodesic flow in the doubled geometry. Inspired by analysis on the particle motion, we propose a modified model of quantum string cosmology, which includes two scale factors. The report is based on Phys. Rev. D84 (2011) 124049 [arXiv:1108.5795].
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.
We study the deconstructed scalar theory having nonlinear interactions and being renormalizable. It is shown that the kink-like configurations exist in such models. The possible forms of Yukawa coupling are considered. We find the degeneracy in mass spectrum of fermions coupled to the nontrivial scalar configuration.
In double field theory, the equation of motion for a point particle in the background field is considered. We find that the motion is described by a geodesic flow in the doubled geometry. Inspired by the analysis on the particle motion, we consider a modified model of quantum string cosmology, which includes two scale factors.
We study UV-finite theory of induced gravity. We use scalar fields, Dirac fields and vector fields as matter fields whose one-loop effects induce the gravitational action. To obtain the mass spectrum which satisfies the UV-finiteness condition, we use a graph-based construction of mass matrices. The existence of a self-consistent static solution for an Einstein universe is shown in the presence of degenerate fermion.
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.
Recently, a multigraviton theory on a simple closed circuit graph corresponding to the discretization of $S^1$ compactification of the Kaluza-Klein (KK) theory has been considered. In the present paper, we extend this theory to that on a general graph and study what modes of particles are included. Furthermore, we generalize it in a possible nonlinear theory based on the vierbein formalism and study classical and quantum cosmological solutions in the theory. We found that scale factors in a solution for this theory repeat acceleration and deceleration.
We extend the dimensional deconstruction by utilizing the knowledge of graph theory. In the dimensional deconstruction, one uses the moose diagram to exhibit the structure of the `theory space'. We generalize the moose diagram to a general graph with oriented edges. In the present paper, we consider only the U(1) gauge symmetry. We also introduce supersymmetry into our model by use of superfields. We suppose that vector superfields reside at the vertices and chiral superfields at the edges of a given graph. Then we can consider multi-vector, multi-Higgs models. In our model, $[U(1)]^p$ (where $p$ is the number of vertices) is broken to a single U(1). Therefore for specific graphs, we get vortex-like classical solutions in our model. We show some examples of the graphs admitting the vortex solutions of simple structure as the Bogomolnyi solution.
We examine cancellation of long-range forces in Einstein-Maxwell-Dilatonic system. Several conditions of the equilibrium of two charged masses in general relativity is found by many authors. These conditions are altered by taking account of dilatonic field. Under the new condition, we show cancellation of $1/r^2$ potential using Feynman diagrams.