ORBIFOLDS OF M-THEORY

We study Z(2)-orbifolds of 11-dimensional M-theory on tori of various dimensions. The most interesting model (besides the known S-1/Z(2) cas e) corresponds to T-5/Z(2), for which we argue that the resulting six- dimensional theory is equivalent to the type IIB string compactified o n K3. Gravitational anomaly cancellation plays a crucial role in deter mining what states appear in the twisted sector, Most of the other mod els appear to break spacetime supersymmetry. We observe that M-theory tends to produce chiral compactifications on orbifolds, and that our r esults may provide an insight into the mechanism by which twisted-sect or states arise in this hypothetical theory.