Ghosts in asymmetric brane gravity and the decoupled stealth limit

TL;DR

This paper analyzes gravitational perturbations in an asymmetric 5D braneworld model with a de Sitter brane, revealing the presence of a ghost mode in most cases, but identifying a limit where it decouples.

Contribution

It extends the stealth acceleration model to asymmetric branes with de Sitter geometry, showing the conditions under which ghost instabilities occur or decouple.

Findings

Ghost propagates on de Sitter branes with infinite bulk volume

Ghost decouples as de Sitter curvature approaches zero

Contrast with Minkowski brane case where no ghost appears

Abstract

We study the spectrum of gravitational perturbations around a vacuum de Sitter brane in a 5D asymmetric braneworld model, with induced curvature on the brane. This generalises the stealth acceleration model proposed by Charmousis, Gregory and Padilla (CGP) which realises the Cardassian cosmology in which power law cosmic acceleration can be driven by ordinary matter. Whenever the bulk has infinite volume we find that there is always a perturbative ghost propagating on the de Sitter brane, in contrast to the Minkowski brane case analysed by CGP. We discuss the implication of this ghost for the stealth acceleration model, and identify a limiting case where the ghost decouples as the de Sitter curvature vanishes.