Gauge-invariant gravitational wave modes in pre-big bang cosmology

TL;DR

This paper analyzes gravitational wave instabilities in pre-big bang cosmology using a gauge-invariant formalism, interpreting the instability as antifriction and discussing the transition to expansion.

Contribution

It applies Hwang's covariant gauge-invariant formalism to pre-big bang scenarios, providing a simple interpretation of tensor perturbation instability as antifriction.

Findings

Identifies gravitational wave instability in the t<0 phase

Interprets instability as antifriction effect

Suggests universe transitions to an expanding phase

Abstract

The t<0 branch of pre-big bang cosmological scenarios is subject to a gravitational wave instability. The unstable behaviour of tensor perturbations is derived in a very simple way in Hwang's covariant and gauge-invariant formalism developed for extended theories of gravity. A simple interpretation of this instability as the effect of an "antifriction" is given, and it is argued that a universe must eventually enter the expanding phase.