Geometric couplings and brane supersymmetry breaking

Orientifold vacua allow the simultaneous presence of supersymmetric bulks, with one or more gravitinos, and nonsupersymmetric combinations of BPS branes. This brane supersymmetry breaking raises the issue of consistency for the resulting gravitino couplings, and Dudas and Mourad recently provided convincing arguments to this effect for the ten-dimensional USp(32) model. These rely on a nonlinear realization of local supersymmetry a la Volkov-Akulov, although no gravitino mass term is present, and the couplings have a nice geometrical interpretation in terms of dressed bulk fields, aside from a Wess-Zumino-like term, resulting from the supersymmetrization of the Chern-Simons. couplings. Here we show that all couplings can be given a geometrical interpretation, albeit in the dual 6-form model, whose bulk includes a Wess-Zumino term, so that the nongeometric ones are in fact demanded by the geometrization of their duals. We also determine the low-energy couplings for six-dimensional (1, 0) models with brane supersymmetry breaking. Since these include both Chem-Simons and Wess-Zumino terms, only the resulting field equations are geometrical, aside from contributions due to vectors of supersymmetric sectors. (C) 2001 Elsevier Science B.V. All rights reserved.