Rotational inhomogeneities from pre-big bang?

TL;DR

This paper investigates the evolution of rotational inhomogeneities in pre-big bang models, finding that non-minimal models can amplify these fluctuations during the pre-big bang phase, but they tend to decay afterward.

Contribution

It provides a detailed analysis of rotational inhomogeneities in both minimal and non-minimal pre-big bang scenarios, including the effects of fluid sources and dilaton potentials.

Findings

Rotational inhomogeneities are not amplified in minimal scenarios.

Non-minimal models can amplify rotational modes depending on fluid properties.

Amplified rotational inhomogeneities decay after the pre-big bang phase.

Abstract

The evolution of the rotational inhomogeneities is investigated in the specific framework of four-dimensional pre-big bang models. While minimal (dilaton-driven) scenarios do not lead to rotational fluctuations, in the case of non-minimal (string-driven) models, fluid sources are present in the pre-big bang phase. The rotational modes of the geometry, coupled to the divergenceless part of the velocity field, can then be amplified depending upon the value of the barotropic index of the perfect fluids. In the light of a possible production of rotational inhomogeneities, solutions describing the coupled evolution of the dilaton field and of the fluid sources are scrutinized in both the string and Einstein frames. In semi-realistic scenarios, where the curvature divergences are regularized by means of a non-local dilaton potential, the rotational inhomogeneities are amplified during the pre-big bang phase but they decay later on. Similar analyses can also be performed when a contraction occurs directly in the string frame metric.