D=4, N=1 orientifolds with vector structure Original Research Artic

We construct compact type IIB orientifolds with discrete groups Z4, Z6, Z6′, Z8, Z12 and Z12′. These models are N=1 supersymmetric in D=4 and have vector structure. The possibility of having vector structure in ZN orientifolds with even N arises due to an alternative Ω-projection in the twisted sectors. Some of the models without vector structure are known to be inconsistent because of uncancelled tadpoles. We show that vector structure leads to a sign flip in the twisted Klein bottle contribution. As a consequence, all the tadpoles can be cancelled by introducing D9-branes and D5-branes.