Shozo Uehara

Rolling down to D-brane and tachyon matter

We investigate the spatially inhomogeneous decay of an unstable D-brane and construct an asymptotic solution which describes a codimension one D-brane and the tachyon matter in boundary string field theory. In this solution, the tachyon matter exists around the lower-dimensional D-brane.

Gauge fields on tachyon matter

We study the rolling tachyon including the gauge fields in boundary string field theory. We show that there are no plane-wave solutions for the gauge fields for large time. The disappearance of the plane-wave solutions indicates that there are no excitations of the gauge fields on the tachyon matter, which is consistent with the Sens conjecture.

On the strong coupling region in quantum matrix string theory

We study the behavior of matrix string theory in the strong coupling region, where matrix strings reduce to discrete light-cone type-IIA superstrings except at the usual string-interaction points. In the large-N limit, this reduction corresponds to the double- dimensional reduction from wrapped supermembranes onR 10 £S 1 to type-IIA superstrings on R 10 in the light-cone gauge. Such reductions were shown classically, while they are not obvious quantum mechanically. Recently, Sekino and Yoneya analyzed the double- dimensional reduction of the wrapped supermembrane quantum mechanically to one-loop order in the strong coupling expansion. We analyze the problem in matrix string theory by using the same expansion. At the one-loop level, the quantum corrections cancel out as was presented by them. However, at the two-loop level we flnd that the quantum corrections cancel out only for the leading terms in the large N.

From supermembrane to super-Yang–Mills theory

Abstract We derive ( p + 1 ) -dimensional ( p = 1 , 2) maximally supersymmetric U ( N ) Yang–Mills theory from the wrapped supermembrane on R 11 − p × T p in the light-cone gauge by using the matrix regularization. The elements of the matrices in the super-Yang–Mills theory are given by the Fourier coefficients in the supermembrane theory. Although our approach never refers to both D-branes and superstring dualities, we obtain the relations which exactly represent T-duality.

Large N Structure of the IIB Matrix Model

We study large N behavior of the IIB matrix model using the equivalence between the IIB matrix model for finite N and a field theory on a non-commutative periodic lattice with N × N sites. We find that the large N dependences of correlation functions can be obtained by naively counting the number of fields in the field theory on a non-commutative periodic lattice. Furthermore, the large N scaling behavior of the coupling constant g is determined if we require that the expectation values of Wilson loops be calculable.

On the DLCQ as a light-like limit in string theory

Abstract We study the issue of defining the discrete light-cone quantization (DLCQ) in perturbative string theory as a light-like limit. While this limit is unproblematic at the classical level, it is non-trivial at the quantum level due to the divergences by the zero-mode loops. We reconsider this problem in bosonic string theory. We construct the multi-loop scattering amplitudes in both open and closed string theories by using the method of Kikkawa, Sakita and Virasoro (KSV), and then we show that these scattering amplitudes are perfectly well-defined in this limit. We also discuss the vacuum amplitudes of the string theory. They are, however, ill-defined in the light-like limit due to the zero-mode loop divergences, and hence we want supersymmetry to cure those pathological divergences even in string theory.

Wrapped membranes, matrix string theory and an infinite dimensional Lie algebra

We examine the algebraic structure of the matrix regularization for the wrapped membrane on 10 ? S1 in the light-cone gauge. We give a concrete representation for the algebra and obtain the matrix string theory having the boundary conditions for the matrix variables corresponding to the wrapped membrane, which is referred to neither Seiberg and Sens arguments nor string dualities. We also embed the configuration of the multi-wrapped membrane in matrix string theory.

Comments on the global constraints in light-cone string and membrane theories

In the light-cone closed string and toroidal membrane theories, we associate the global constraints with gauge symmetries. In the closed string case, we show that the physical states defined by the BRS charge satisfy the level-matching condition. In the toroidal membrane case, we show that the Faddeev-Popov ghost and anti-ghost corresponding to the global constraints are essentially free even if we adopt any gauge fixing condition for the local constraint. We discuss the quantum double-dimensional reduction of the wrapped supermembrane with the global constraints.

(p,q)-string in the wrapped supermembrane on 2-torus: A classical analysis of the bosonic sector

Abstract We consider a wrapped supermembrane on R 9 × T 2 . We examine a double dimensional reduction to deduce a ( p , q ) -string in type IIB superstring theory from the wrapped supermembrane. In particular, directly from the wrapped supermembrane action, we explicitly derive the action of a string which carries the RR 2-form charge as well as the NSNS 2-form charge, and the tension of the string agrees with the ( p , q ) -string tension.

DOES DLCQ S-MATRIX HAVE A COVARIANT CONTINUUM LIMIT?

We develop a systematic DLCQ perturbation theory and show that DLCQ S-matrix does not have a covariant continuum limit for processes with