Large N gauge theories from orientifolds with NS-NS B-flux

We consider D-branes and orientifold planes embedded in non-compact (orbifo lded) space-time. We point out that even in the non-compact cases we can tu rn on non-zero (quantized) NS-NS antisymmetric B-field. In particular, we s tudy the effect of the B-field on four-dimensional large N gauge theories f rom orientifolds. Thus, in theories with both D3- and D7-branes, the effect of the B-field is non-trivial: the number of D7-branes (of each species) i s reduced from 8 (which is the required number if the B-field is trivial) t o 4. This results in a different orientifold string theory, and, subsequent ly, the corresponding large N gauge theory is also different. We explicitly construct large N gauge theories from orientifolds with non-zero B-field b ackgrounds with N = 2, 1, 0 supersymmetries. These theories, just as their counterparts without the B-field, have the property that in the large N lim it computation of any M-point correlation function reduces to the correspon ding computation in the parent N = 4 supersymmetric theory with a unitary g auge group. (C) 1999 Elsevier Science B.V.