D = 4, N = 1, type IIB orientifolds Original Research Article

We study different aspects of the construction of D = 4, N = 1 type IIB orientifolds based on toroidal ZN and ZM × ZN, D = 4 ortifolds. We find that tadpole cancellation conditions are in general more constraining than in six dimensions and that the standard Gimon-Polchinski orientifold projection leads to the impossibility of tadpole cancellations in a number of ZN orientifolds with even N including Z4, Z8, Z8′ and Z12′. We construct D = 4, ZN and ZN × ZM orientifolds with different configurations of 9-branes, 5-branes and 7-branes, most of them chiral. Models including the analogue of discrete torsion are constructed and shown to have features previously conjectured on the basis of F-theory compactified on four-folds. Different properties of the D = 4, N = 1 models obtained are discussed including their possible heterotic duals and effective low-energy action. These models have in general more than one anomalous U(1) and the anomalies are cancelled by a D = 4 generalized Green-Schwarz mechanism involving dilaton and moduli fields.