arXiv subjects
Publications and source records attributed to Nahomi Kan.
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.
Long-range forces up to next-to-leading order are computed in the framework of the Einstein-Maxwell-dilaton system by means of a semiclassical approach to gravity. As has been recently shown, this approach is effective if one of the masses under consideration is significantly greater than all the energies involved in the system. Further, we obtain the condition for the equilibrium of charged masses in the system.
We study self-consistent static solutions for an Einstein universe in a graph-based induced gravity. In the generalization of the deconstruction model based on the graph, the eigenvalues of the graph Laplacian and the adjacent matrix gives the mass spectrum the particles. Thus we can easily control UV divergences at one-loop level in such a model. We use the calculation method with the spectrum distribution function of the graph and search for the static solution supported by the degenerate pressure of the fermion (at zero temperature). The report is based on arXiv:1110.5697.
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.
Weyl invariant gravity has been investigated as the fundamental theory of the vector inflation. Accordingly, we consider a Weyl invariant extension of Dirac-Born-Infeld type gravity. We find that an appropriate choice of the metric removes the scalar degree of freedom which is at the first sight required by the local scale invariance of the action, and then a vector field acquires mass. Then nonminimal couplings of the vector field and curvatures are induced. We find that the Dirac-Born-Infeld type gravity is a suitable theory to the vector inflation scenario.
We consider a Weyl invariant extension of Dirac-Born-Infeld type gravity. An appropriate choice of the metric hides the scalar degree of freedom which is required by the local scale invariance of the action at the first sight, and then a vector field acquires mass. Moreover, nonminimal couplings of the vector field and curvatures are induced, which may be suitable to the vector inflation scenario.
We study solutions for boson stars in multiscalar theory. We start with simple models with N scalar theories. Our purpose is to study the models in which the mass matrix of scalars and the scalar couplings are given by an extended method of dimensional deconstruction. The properties of the boson stars are investigated by the Newtonian approximation with the large coupling limit.
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.
We study self-consistent static solutions for an Einstein universe in a graph-based induced gravity. The one-loop quantum action is computed at finite temperature. In particular, we demonstrate specific results for the models based on cycle graphs.
We study self-consistent cosmological solutions for an Einstein Universe in a graph-based induced gravity model. The graph-based field theory has been proposed by the present authors to generalize dimensional deconstruction. In this paper, we consider self-consistent Einstein equations for a ``graph theory space''. Especially, we demonstrate specific results for cycle graphs.