Gauge-invariant gravitational wave modes in pre-big bang cosmology
arXiv:1009.0660 · doi:10.1140/epjc/s10052-010-1445-9
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.
4 pages, latex, to appear in Eur. Phys. J. C