Metastable string vacua

We argue that tachyon-free type I string vacua with supersymmetry breaking in the open sector at the string scale can be interpreted, via S- and T-duality arguments, as metastable vacua of the supersymmetric type I superstring. The dynamics of the process can be partly captured via nucleation of brane–anti-brane pairs out of the non-supersymmetric vacuum and subsequent tachyon condensation.