Nonsingular Bianchi type I cosmological solutions from 1-loop superstring effective action

TL;DR

This paper derives non-singular anisotropic Bianchi type I cosmological solutions from a superstring-inspired effective action incorporating a Gauss-Bonnet term, revealing smooth evolutions and a new type of singularity related to anisotropic expansion rates.

Contribution

It introduces novel non-singular Bianchi type I solutions from superstring effective action with a Gauss-Bonnet term, including the discovery of a new singularity type linked to anisotropic expansion.

Findings

Solutions evolve from Minkowski space to super-inflation and then to Kasner or Friedmann regimes.

Identifies a new singularity arising from multiple-valued anisotropic expansion rates.

Steep super-inflation may lead to singularities in anisotropic solutions.

Abstract

Non-singular Bianchi type I solutions are found from the effective action with a superstring-motivated Gauss-Bonnet term. These anisotropic non-singular solutions evolve from the asymptotic Minkowski region, subsequently super-inflate, and then smoothly continue either to Kasner-type (expanding in two directions and shrinking in one direction) or to Friedmann-type (expanding in all directions) solutions. We also found a new kind of singularity which arises from the fact that the anisotropic expansion rates are multiple-valued function of time. The initial singularity in the isotropic limit of this model belongs to this new kind of singularity. In our analysis the anisotropic solutions are likely to be singular when the super-inflation is steep.