Consistent gravitino couplings in non-supersymmetric strings

The massless spectrum of the ten-dimensional USp(32) type I string has an N = 1 supergravity multiplet coupled to nonsupersymmetric matter. This raises the question of the consistency of the gravitino interactions. We resolve this apparent puzzle by arguing for the existence of a local supersymmetry which is non-linearly realised in the open sector. We determine the leading order low energy effective Lagrangian. Similar results are expected to apply to lower dimensional type I models where supergravity is coupled to non-supersymmetric branes. (C) 2001 Elsevier Science B.V. All rights reserved.