Anomaly cancelations in orientifolds with quantized B-flux

We consider anomaly cancelations in Type IIB orientifolds on T-4/Z(N) with quantized NS-NS sector background B-flux. For a rank b B-flux on T-4 (b is always even) and when N is even, the cancelation requires a 2(b/2) multipli city of states in the 59-open string sector. We identify the twisted sector R-R scalars and tensor multiplets which are involved in the Green-Schwarz mechanism. We give more details of the construction of these models and arg ue that consistency with the 2(b/2) multiplicity of 59-sector states requir es a modification of the relation between the open string I-loop channel mo dulus and the closed string tree channel modulus in the 59-cylinder amplitu des. (C) 2000 Elsevier Science B.V. All rights reserved.