Aspects of ALE matrix models and twisted matrix strings

We examine several aspects of the formulation of M(atrix)-theory on ALE spaces. We argue for the existence of massless vector multiplets in the resolved A(n-1) spaces, as required by enhanced gauge symmetry in M-theory, and that these states might have the correct gravitational interactions. We propose a matrix model which describes M-theory on an ALE space in the presence of wrapped membranes. We also consider orbifold descriptions of matrix string theories, as well as more exotic orbifolds of these models, and present a classification of twisted matrix string theories according to Reid's exact sequences of surface quotient singularities. [S0556-2821(98)07414-1].