Maximally Symmetric Cosmological Solutions of Type II Superstrings

Abstract

We study maximally symmetric cosmological solutions of type II supersymmetric strings in the presence of the exact, SL(2,Z)-invariant, higher-curvature corrections to the lowest order effective action. We find that, unlike the case of type IIA theories, de Sitter solutions exist, at all orders in ${\alpha }^{\prime }$, for type IIB superstrings, when non-perturbative instanton-effects are included on the basis of SL(2,Z) invariance.

5 pages, Latex, no figures, talk presented at "New Worlds in Astroparticle Physics" 1998, Faro, Portugal