Cosmological Solutions of Type II String Theory

TL;DR

This paper explores cosmological solutions in type II string theory with nontrivial Ramond-Ramond forms, revealing integrable models and phases of superinflation and subluminal expansion separated by singularities.

Contribution

It provides exact solutions for models with one or two Ramond-Ramond forms, including Toda model solutions, advancing understanding of string cosmology dynamics.

Findings

Identified integrable cosmological models with one or two forms.

Discovered solutions with superinflating and subluminal expanding phases.

Showed forms interpolate between different Kaluza-Klein solutions.

Abstract

We study cosmological solutions of type II string theory with a metric of the Kaluza--Klein type and nontrivial Ramond--Ramond forms. It is shown that models with only one form excited can be integrated in general. Moreover, some interesting cases with two nontrivial forms can be solved completely since they correspond to Toda models. We find two types of solutions corresponding to a negative time superinflating phase and a positive time subluminal expanding phase. The two branches are separated by a curvature singularity. Within each branch the effect of the forms is to interpolate between different solutions of pure Kaluza--Klein theory.