On R^4 terms and MHV amplitudes in N = 5,6 supergravity vacua of Type II superstrings

摘要

We compute one-loop threshold corrections to R^4 terms in N= 5,6 supergravityvacua of Type II superstrings. We then discuss non-perturbative correctionsgenerated by asymmetric D-brane instantons. Finally we derive generatingfunctions for MHV amplitudes at tree level in N = 5, 6 supergravities.