Ghost-free braneworld bigravity

TL;DR

This paper develops a generalized braneworld bigravity model with two branes, analyzing fluctuations to identify ghost-free configurations that could produce observable modifications to gravity at large distances.

Contribution

It introduces a new bigravity model with two branes, localised curvature, and tunable parameters to avoid ghosts and tachyons, expanding the landscape of viable modified gravity theories.

Findings

Identified parameter regimes with ghost-free, tachyon-free bigravity models.

Demonstrated potential for large-distance gravity modifications.

Provided detailed analysis of radion and graviton fluctuations.

Abstract

We consider a generalisation of the DGP model, by adding a second brane with localised curvature, and allowing for a bulk cosmological constant and brane tensions. We study radion and graviton fluctuations in detail, enabling us to check for ghosts and tachyons. By tuning our parameters accordingly, we find bigravity models that are free from ghosts and tachyons. These models will lead to large distance modifications of gravity that could be observable in the near future.