Infra-red modification of gravity from asymmetric branes

TL;DR

This paper investigates how asymmetric brane configurations in anti-de Sitter space can lead to modifications of gravity at large scales, addressing tensor structure issues and stability concerns.

Contribution

It introduces a model with asymmetric bulk properties that modifies gravity in the infra-red and analyzes the tensor structure and stability of perturbations.

Findings

Gravity is modified at large scales with correct momentum dependence.

Tensor structure of the graviton propagator is corrected by brane bending effects.

No evidence of scalar ghosts or strong coupling issues up to high energies.

Abstract

We consider a single Minkowski brane sandwiched in between two copies of anti-de Sitter space. We allow the bulk Planck mass and cosmological constant to differ on either side of the brane. Linearised perturbations about this background reveal that gravity can be modified in the infra-red. At intermediate scales, the braneworld propagator mimics four-dimensional GR in that it has the correct momentum dependance. However it has the wrong tensor structure. Beyond a source dependant scale, we show that quadratic brane bending contributions become important, and conspire to correct the tensor structure of the propagator. We argue that even higher order terms can consistently be ignored up to very high energies, and suggest that there is no problem with strong coupling. We also consider scalar and vector perturbations in the bulk, checking for scalar ghosts.