Brane-antibrane constructions

In type-II string theories, we examine intersecting brane constructions con taining brane-antibrane pairs suspended between 5-branes, and more general non-BPS constructions. The tree-level spectra are obtained in each case. We identify various models with distinct physics: parallel brane-antibrane pa irs, adjacent pairs, non-adjacent pairs, and configurations which break all supersymmetry even though any pair of branes preserves some supersymmetry. In each case we examine the possible decay modes. Some of these configurat ions turn out to be tachyon-free, stable non-BPS states. We use T-duality t o map some of our brane constructions to brane-antibrane pairs at ALE singu larities. This enables us to explicitly derive the spectra by the analogue of the quiver construction, and to compute the sign of the brane-antibrane force in each case.