Matrix string theory and its moduli space

The correspondence between Matrix String Theory in the strong coupling limit and IIA superstring theory can be shown by means of the instanton solutions of the former. We construct the general instanton solutions of Matrix String Theory which interpolate between given initial and final string configurations. Each instanton is characterized by a Riemann surface of genus h with n punctures, which is realized as a plane curve. We study the moduli space of such plane curves and find out that, at finite N, it is a discretized version of the moduli space of Riemann surfaces: instead of 3h - 3 + n its complex dimensions are 2h - 3 + n, the remaining h dimensions being discrete. It turns out that as N tends to infinity, these discrete dimensions become continuous. We argue that in this limit one recovers the full moduli space of string interaction theory. © 1999 Elsevier Science B.V. All rights reserved.