A Non-Singular Universe in String Cosmology

TL;DR

This paper presents an exact non-singular cosmological solution derived from string theory's low-energy effective action, showing a universe that avoids initial singularity with specific tensor field behavior and modified energy conditions.

Contribution

It introduces a new exact homogeneous solution in string cosmology that models a non-singular, expanding universe with vanishing tensor fields at late times.

Findings

The scale factor follows a(t)^2 = a_0^2 + t^2.

The solution avoids the initial singularity by violating classical energy conditions.

Tensor fields tend to vanish as t approaches infinity.

Abstract

We consider the low-energy effective string action in four dimensions including the leading order-$\alpha'$ terms. An exact homogeneous solution is obtained. It represents a non-singular expanding cosmological model in which the tensor fields tend to vanish as $t\to \infty$. The scale factor $a(t)$ of the very early universe in this model has the time dependence $a(t)^2=a_0^2+t^2$. The violation of the strong energy condition of classical General Relativity to avoid the initial singularity requires that the central charge deficit of the theory be larger than a certain value. The significance of this solution is discussed.