Self-accelerating Warped Braneworlds

TL;DR

This paper introduces a broad class of warped braneworld models with induced gravity, exploring their ghost issues and potential to explain cosmic acceleration without dark energy.

Contribution

It generalizes the DGP model by including negative bulk curvature, multiple branes, and various brane tensions, analyzing ghost phenomena and their relation to self-acceleration.

Findings

Identifies three types of ghosts linked to different graviton modes.

Shows correlation between DGP ghosts and model parameters.

Suggests models as a platform to understand and possibly eliminate ghosts.

Abstract

Braneworld models with induced gravity have the potential to replace dark energy as the explanation for the current accelerating expansion of the Universe. The original model of Dvali, Gabadadze and Porrati (DGP) demonstrated the existence of a ``self--accelerating'' branch of background solutions, but suffered from the presence of ghosts. We present a new large class of braneworld models which generalize the DGP model. Our models have negative curvature in the bulk, allow a second brane, and have general brane tensions and localized curvature terms. We exhibit three different kinds of ghosts, associated to the graviton zero mode, the radion, and the longitudinal components of massive graviton modes. The latter two species occur in the DGP model, for negative and positive brane tension respectively. In our models, we find that the two kinds of DGP ghosts are tightly correlated with each other, but are not always linked to the feature of self--acceleration. Our models are a promising laboratory for understanding the origins and physical meaning of braneworld ghosts, and perhaps for eliminating them altogether.