BPS states in superstrings with spontaneously broken SUSY (N=4->N=2->N=1)

We show the existence of a supersymmetry-breaking mechanism in string theory, where N = 4 supersymmetry is broken spontaneously to N = 2 and N = 1 with moduli-dependent gravitino masses., The BPS spectrum of the theory with lower supersymmetry is in one-to-one correspondence with the spectrum of the heterotic N = 4 string. The mass splitting of the N = 4 spectrum depends on the moduli as well as the three R-symmetry charges. In the case of N = 4 --> N = 2, the perturbative N = 2 prepotential is determined by the perturbative N = 4 BPS states. This observation led us to suggest a method that determines the exact non-perturbative prepotential of the effective N = 2 supergravity using the shifted spectrum of the non-perturbative BPS states of the underlying N = 4 theory.