arXiv subjects

Shinsuke Kawai

Publications and source records attributed to Shinsuke Kawai.

47 records · Page 3Linked to original sources

arXiv2003

Free boson formulation of boundary states in W_3 minimal models and the critical Potts model

We develop a Coulomb gas formalism for boundary conformal field theory having a $W$ symmetry and illustrate its operation using the three state Potts model. We find that there are free-field representations for six $W$ conserving boundary states, which yield the fixed and mixed physical boundary conditions, and two $W$ violating boundary states which yield the free and new boundary conditions. Other $W$ violating boundary states can be constructed but they decouple from the rest of the theory. Thus we have a complete free-field realization of the known boundary states of the three state Potts model. We then use the formalism to calculate boundary correlation functions in various cases. We find that the conformal blocks arising when the two point function of $ϕ_{2,3}$ is calculated in the presence of free and new boundary conditions are indeed the last two solutions of the sixth order differential equation generated by the singular vector.

hep-th↗

arXiv2003

Free-field realisation of boundary states and boundary correlation functions of minimal models

We propose a general formalism to compute exact correlation functions for Cardy's boundary states. Using the free-field construction of boundary states and applying the Coulomb-gas technique, it is shown that charge-neutrality conditions pick up particular linear combinations of conformal blocks. As an example we study the critical Ising model with free and fixed boundary conditions, and demonstrate that conventional results are reproduced. This formalism thus directly associates algebraically constructed boundary states with correlation functions which are in principle observable or numerically calculable.

hep-th↗

arXiv2003

Logarithmic conformal field theory with boundary

This lecture note covers topics on boundary conformal field theory, modular transformations and the Verlinde formula, and boundary logarithmic CFT. An introductory review on CFT with boundary and a discussion of its applications to logarithmic cases are given. LCFT at $c=-2$ is mainly discussed.

hep-th↗

arXiv2002

Coulomb-gas approach for boundary conformal field theory

We present a construction of boundary states based on the Coulomb-gas formalism of Dotsenko and Fateev. It is shown that Neumann-like coherent states on the charged bosonic Fock space provide a set of boundary states with consistent modular properties. Such coherent states are characterised by the boundary charges, which are related to the number of bulk screening operators through the charge neutrality condition. We illustrate this using the Ising model as an example, and show that all of its known consistent boundary states are reproduced in our formalism. This method applies to $c<1$ minimal conformal theories and provides an unified computational tool for studying boundary states of such theories.

hep-th↗

arXiv2001

Modular transformation and boundary states in logarithmic conformal field theory

We study the $c=-2$ model of logarithmic conformal field theory in the presence of a boundary using symplectic fermions. We find boundary states with consistent modular properties. A peculiar feature of this model is that the vacuum representation corresponding to the identity operator is a sub-representation of a ``reducible but indecomposable'' larger representation. This leads to unusual properties, such as the failure of the Verlinde formula. Despite such complexities in the structure of modules, our results suggest that logarithmic conformal field theories admit bona fide boundary states.

hep-th↗

arXiv1999

Structure Formation in Non-singular Higher Curvature Cosmology

We propose novel structure formation scenarios based on a non-singular higher curvature cosmological model. The model is motivated by the $R^2$ coupling of a scalar field appearing in the string theory, and in our scenarios the universe has no beginning and no end. We give two examples with explicit parameter values which are consistent with present observations of the cosmological structure. In the first example, the origin of structures are generated as the adiabatic perturbation during the chaotic inflation, while in the second the isocurvature non-Gaussian perturbation from the superinflating era is responsible for the structure. In the second case it is possible to generate primordial supermassive blackholes whose scale is comparable to what is expected in the galactic nuclei.

gr-qc↗

arXiv1999

Evolution of Fluctuations during Graceful Exit in String Cosmology

We study the evolution of fluctuations in a universe dominated by a scalar field coupled to the Gauss-Bonnet term. During the graceful exit, we found non-negligible enhancements of both curvature perturbation and gravitational wave in the long wavelength limit, and we also found a short wavelength instability for steep background superinflation just after the completion of the graceful exit. This result for one possible graceful exit mechanism would provide a significant implication on the primordial spectrum from the string cos mology.

gr-qc↗

arXiv1999

Perturbative analysis of non-singular cosmological model

A stability analysis is made for a non-singular pre-big-bang like cosmological model based on 1-loop corrected string effective action. Its homogeneous and isotropic solution realizes non-singular transition from de Sitter universe to Friedmann-like universe, via super inflation phase. We are interested in whether the non-singular nature of the solution would be stable or not in more general inhomogeneous case. Perturbative analysis is made for scalar, vector, and tensor linear perturbations, and instability is found for tensor-type perturbation.

gr-qc↗

arXiv1999

Nonsingular Bianchi type I cosmological solutions from 1-loop superstring effective action

Non-singular Bianchi type I solutions are found from the effective action with a superstring-motivated Gauss-Bonnet term. These anisotropic non-singular solutions evolve from the asymptotic Minkowski region, subsequently super-inflate, and then smoothly continue either to Kasner-type (expanding in two directions and shrinking in one direction) or to Friedmann-type (expanding in all directions) solutions. We also found a new kind of singularity which arises from the fact that the anisotropic expansion rates are multiple-valued function of time. The initial singularity in the isotropic limit of this model belongs to this new kind of singularity. In our analysis the anisotropic solutions are likely to be singular when the super-inflation is steep.

gr-qc↗

arXiv1998

Novel Instability in Superstring Cosmology

As a most promising candidate for quantum theory of the gravity, the superstring theory has attracted many researchers including cosmologists. It is expected that the cosmological initial singularity is avoided within the context of the superstring theory. Indeed, Antoniadis et. al. found an interesting example of the non-singular cosmological solutions by considering the string one-loop correction. Here, we will discuss the stability of this model and find a new kind of instability in the graviton modes. We also argue this instability will persist even in the non-perturbative regime. The instability we have found might provide a mechanism to produce the primodial black holes.

gr-qc↗

arXiv1998

Instability of 1-loop superstring cosmology

A stability analysis is made in the context of the previously discovered non-singular cosmological solution from 1-loop corrected superstring effective action. We found that this solution has an instability in graviton mode, which is shown to have a close relation to the avoidance of initial singularity via energy condition. We also estimate the condition for the breakdown of the background solution due to the overdominance of the graviton.

gr-qc↗