M(atrix) Theory on an Orbifold and Twisted Membrane M(atrix) Theory on an Orbifold and Twisted Membrane 1

M(atrix) theory on an orbifold and classical two-branes therein are studied with particular emphasis to heterotic M(atrix) theory on S1=Z2 relevant to strongly coupled heterotic and dual Type IA string theories. By analyzing orbifold condition on Chan-Paton factors, we show that three choice of gauge group are possible for heterotic M(atrix) theory: SO(2N), SO(2N + 1) or USp(2N). By examining area-preserving di eomorphism that underlies the M(atrix) theory, we nd that each choices of gauge group restricts possible topologies of twobranes. The result suggests that only the choice of SO(2N) or SO(2N +1) groups allows open two-branes, hence, relevant to heterotic M(atrix) theory. We show that requirement of both local vacuum energy cancellation and of worldsheet anomaly cancellation of resulting heterotic string identi es supersymmetric twisted sector spectra with sixteen fundamental representation spinors from each of the two xed points. Twisted open and closed two-brane con gurations are obtained in the large N limit. Work supported in part by the Department of Energy Contract DE-AC03-76SF00515, NSF Grant PHY9219345, U.S.NSF-KOSEF Bilateral Grant, KOSEF Purpose-Oriented Research Grant 94-1400-04-01-3 and SRC-Program, Ministry of Eduction Grant BSRI 97-2410 and the Seoam Foundation Fellowship.