BPS Spectra and Non--Perturbative Couplings in N=2,4 Supersymmetric String Theories

Gabriel Lopes Cardoso, Gottfried Curio, Dieter Lust +2

We study the BPS spectrum in $D=4,N=4$ heterotic string compactifications, with some emphasis on intermediate $N=4$ BPS states. These intermediate states, which can become short i…