Low-energy graceful exit in anisotropic string cosmology backgrounds

TL;DR

This paper explores conditions under which a smooth transition from pre- to post-big bang in string cosmology can occur, emphasizing the role of anisotropic, higher-dimensional backgrounds and quantum fluctuation effects.

Contribution

It demonstrates that a realistic, smooth transition is possible in anisotropic, higher-dimensional string backgrounds with quantum fluctuation back-reaction effects, without higher-derivative corrections.

Findings

Smooth transition conditions are satisfied in higher-dimensional anisotropic models.

Quantum fluctuations outside the horizon can induce repulsive gravity effects.

A phenomenological source model enables realistic cosmological evolution.

Abstract

We discuss the possibility of a smooth transition from the pre- to the post-big bang regime, in the context of the lowest-order string effective action (without higher-derivative corrections), taking into account with a phenomenological model of source the repulsive gravitational effects due to the back-reaction of the quantum fluctuations outside the horizon. We determine a set of necessary conditions for a successful and realistic transition, and we find that such conditions can be satisfied (by an appropriate model of source), provided the background is higher-dimensional and anisotropic.