M(ATRIX) THEORY ON AN ORBIFOLD AND TWISTED MEMBRANE

M(atrix) theory on an orbifold and classical two-branes therein are st udied with particular emphasis on heterotic M(atrix) theory on S-1/Z(2 ) relevant to strongly coupled heterotic and dual Type IA string theor ies. By analyzing the orbifold condition on Chan-Paton factors, we sho w that three choices of gauge group are possible for heterotic M(atrix ) theory: SO(2N), SO(2N + 1) or USp(2N). By examining the area-preserv ing diffeomorphism that underlies the M(atrix) theory, we find that ea ch choice of gauge group restricts the possible topologies of two-bran es. The result suggests that only the choice of SO(2N) or SO(2N + 1) a llows open two-branes, and hence, is relevant to heterotic M(atrix) th eory. We show that the requirement of both local vacuum energy cancell ation and of world-sheet anomaly cancellation of the resulting heterot ic string identifies supersymmetric twisted sector spectra with sixtee n fundamental representation spinors from each of the two fixed points . Twisted open and closed two-brane configurations are obtained in the large N limit. (C) 1997 Published by Elsevier Science B.V.