Towards a non-singular pre-big bang cosmology

TL;DR

This paper explores string cosmology equations at all orders in alpha' and shows how certain solutions can serve as regular, non-singular attractors, potentially explaining the transition from pre-big bang to standard cosmology.

Contribution

It provides an explicit example of how alpha' corrections lead to non-singular solutions acting as attractors, supporting a smooth transition in string cosmology.

Findings

Solutions act as late-time regularizing attractors

Explicit example of transition from dilaton to string phase

Discussion on the role of alpha' corrections and string loops

Abstract

We discuss general features of the $\beta$-function equations for spatially flat, $(d+1)$-dimensional cosmological backgrounds at lowest order in the string-loop expansion, but to all orders in $\alpha'$. In the special case of constant curvature and a linear dilaton these equations reduce to $(d+1)$ algebraic equations in $(d+1)$ unknowns, whose solutions can act as late-time regularizing attractors for the singular lowest-order pre-big bang solutions. We illustrate the phenomenon in a first order example, thus providing an explicit realization of the previously conjectured transition from the dilaton to the string phase in the weak coupling regime of string cosmology. The complementary role of $\alpha'$ corrections and string loops for completing the transition to the standard cosmological scenario is also briefly discussed.