Internal magnetic fields and supersymmetry in orientifolds

TL;DR

This work investigates supersymmetric vacua in Type I/II settings with internal magnetic fluxes and discrete torsion. It establishes a brane transmutation via the mapping $H_i \leftrightarrow 1/{\cal H}_i$, enabling equivalent descriptions between magnetized BPS and non-BPS branes, and derives comprehensive SUSY and twisted-tadpole constraints for multiple flux stacks. The authors construct explicit chiral ${Z}_2\times {Z}_2$ orientifolds with discrete torsion, including fractional-brane at fixed points, and provide detailed massless spectra and gauge content, highlighting new twisted RR tadpole conditions. Additionally, they present a nine-dimensional Scherk-Schwarz orientifold with a novel non-BPS O9 plane and softly broken open-string sectors, broadening the landscape of controllable supersymmetry breaking in string theory. These results offer new avenues for magnetized-brane model building and potential links to moduli stabilization frameworks.

Abstract

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 Z_2 x Z_2 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.