Gauss-Bonnet gravity renders negative tension braneworlds unstable

TL;DR

Gauss-Bonnet corrections in gravity cause instability in negative tension braneworlds, leading to a gravitational tachyon mode, which challenges the stability of such models.

Contribution

This paper demonstrates that Gauss-Bonnet terms induce a gravitational tachyon in Randall-Sundrum models with negative tension branes, revealing a new instability mechanism.

Findings

Gauss-Bonnet terms induce a gravitational tachyon mode.

The instability is linked to negative tension branes.

Possible resolutions include induced gravity or cosmological constant.

Abstract

We show that the Gauss-Bonnet correction to Einstein gravity induces a gravitational tachyon mode, namely an unstable spin 2 fluctuation, in the Randall-Sundrum I model. We demonstrate that this instability is generically related to the presence of a negative tension brane in the set-up, with or without $Z_2$-symmetry across it. Indeed it is shown that the tachyon mode is a bound state localised on any negative tension brane of co-dimension one, embedded in anti-de Sitter background. We discuss the possible resolution of this instability by the inclusion of induced gravity terms on the branes or by an effective four-dimensional cosmological constant.