A New Cosmological Scenario in String Theory

TL;DR

This paper introduces new cosmological solutions within string theory featuring collapsing, intermediate, and expanding phases, with potential implications for understanding the universe's evolution and singularity resolution.

Contribution

It presents novel cosmological models embedded in string and M-theory, including a two-dimensional case with a string orbifold and parallels to black hole physics.

Findings

Existence of cosmological solutions with horizon-like boundaries

String orbifold models with modular invariant partition functions

Potential resolution of singularities via light winding modes

Abstract

We consider new cosmological solutions with a collapsing, an intermediate and an expanding phase. The boundary between the expanding (collapsing) phase and the intermediate phase is seen by comoving observers as a cosmological past (future) horizon. The solutions are naturally embedded in string and M-theory. In the particular case of a two-dimensional cosmology, space-time is flat with an identification under boost and translation transformations. We consider the corresponding string theory orbifold and calculate the modular invariant one-loop partition function. In this case there is a strong parallel with the BTZ black hole. The higher dimensional cosmologies have a time-like curvature singularity in the intermediate region. In some cases the string coupling can be made small throughout all of space-time but string corrections become important at the singularity. This happens where string winding modes become light which could resolve the singularity. The new proposed space-time casual structure could have implications for cosmology, independently of string theory.