CONSISTENCY CONDITIONS FOR BRANES AT ORBIFOLD SINGULARITIES

We discuss consistency conditions for branes at orbifold singularities . The conditions have a world-sheet interpretation in terms of tadpole cancellation and a space-time interpretation in terms of anomalies. A s examples, we consider type II and type I branes on C-2/Z(M) orbifold s. We give orientifold constructions of phases of type I or heterotic string theory, involving branches with extra tensor multiplets, which arise when small SO(32) instantons sit on orbifold singularities. (C) 1997 Elsevier Science B.V.