Tree-level String Cosmology

TL;DR

This paper explores the classical evolution of a string theory-derived cosmological model, revealing its equivalence to a scalar field system and analyzing its singularity behavior.

Contribution

It demonstrates the formal equivalence between a string-inspired cosmological model and a scalar field in Einstein gravity, and describes the full range of possible cosmological evolutions.

Findings

Solutions generally begin or end with a singularity.

Approaching singularities, the dilaton field becomes large, indicating the importance of loop corrections.

The model encompasses a variety of cosmological behaviors depending on initial conditions.

Abstract

In this paper we examine the classical evolution of a cosmological model derived from the low-energy tree-level limit of a generic string theory. The action contains the metric, dilaton, central charge and an antisymmetric tensor field. We show that with a homogeneous and isotropic metric, allowing spatial curvature, there is a formal equivalence between this system and a scalar field minimally coupled to Einstein gravity in a spatially flat metric. We refer to this system as the shifted frame and using it we describe the full range of cosmological evolution that this model can exhibit. We show that generic solutions begin (or end) with a singularity. As the system approaches a singularity the dilaton becomes becomes large and loop corrections will become important.