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 largeN limit, this reduction corresponds to the doubledimensional reduction from wrapped supermembranes on R10 × S1 to type IIA superstrings on R10 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 find that the quantum corrections cancel out only for the leading terms in the large N .