TOWARDS A NONPERTURBATIVE FORMULATION OF IIB SUPERSTRINGS BY MATRIX MODELS

We address the problem of a non-perturbative formulation of superstrin g theory by means of the recently proposed matrix models. For the mode l by Ishibashi, Kawai, Kitazawa and Tsuchiya (IKKT), we perform one-lo op calculation of the interaction between operator-like solutions iden tified with D-brane configurations of type IIB superstrings (in partic ular, for parallel moving and rotated static p-branes). Comparing to t he superstring calculations, we show that the matrix model reproduces the superstring results only at small velocities or large distances, c orresponding to keeping only the lowest mass open-string modes, We pro pose a modification of the IKKT matrix model introducing an integratio n over an additional Hermitian matrix required to have positive defini te eigenvalues, which is similar to the square root of the metric in t he continuum Schild formulation of IIB superstrings. We show that for this new matrix action the Nambu-Goto version of the Green-Schwarz act ion is reproduced even at quantum level. (C) 1997 Elsevier Science B.V .