On gauge bosons in the matrix model approach to M theory

We discuss the appearance of E8 × E8 gauge bosons in Banks, Fischler, Shenker, and Susskindʹs zero brane quantum mechanics approach to M theory, compactified on the interval S1Z2. The necessary bound states of zero branes are proven to exist by a straightforward application of T-duality and heterotic Spin(32)/Z2-Type I duality. We then study directly the zero brane Hamiltonian in Type I′ theory. This Hamiltonian includes couplings between the zero branes and background Dirichlet 8 branes licalized at the orientifold planes. We identify states, localized at the orientifold planes, with the requisite gauge boson quantum numbers. An interesting feature is that E8 gauge symmetry relates bound states of different numbers of zero branes.