A new orientifold of C-2/Z(N) and six-dimensional RG fixed points

We discuss the consistency conditions of a novel orientifold projection of type IIB string theory on C-2/Z(N) singularities, in which one mods out by the combined action of world-sheet parity and a geometric operation which e xchanges the two complex planes. The field theory on the, world-volume of D 5-brane probes defines a family of six-dimensional RG fixed points, which h ad been previously constructed using type IIA configurations of NS-branes a nd D6-branes in the presence of O6-planes. Both constructions are related b y a T-duality transforming the set of NS-branes into the C-2/Z(N) singulari ty. We also construct additional models, where both the standard and the no vel orientifold projections are imposed. They have an interesting relation with orientifolds of D-K singularities, and provide the T-duals of certain type IIA configurations containing both O6- and O8-planes. (C) 2000 Elsevie r Science B.V. All rights reserved.