Internal magnetic fields and supersymmetry in orientifolds

Within the context of type I strings, we show the equivalence between BPS D9-branes with internal magnetic fluxes H_i in the three torii and non-BPS D3-branes with inverted internal magnetic fluxes 1/H_i. We then construct new supersymmetric examples of Z² × Z² orientifolds with discrete torsion which in the past had only non-supersymmetric solutions and emphasize the role of new twisted tadpole cancellation conditions, arising in the presence of magnetic fields, in order to get a consistent spectrum. In a second and independent part of the paper, we construct a new nine-dimensional type IIB orientifold with Scherk-Schwarz deformation which has the peculiarity of introducing a new type of non-BPS O9-planes and which contains as top branes a Scherk-Schwarz deformation of non-BPS D9-branes. The model contains charged D7- and D3-branes with a soft supersymmetry breaking spectrum.