Mass-Varying Massive Gravity

TL;DR

This paper introduces a scalar-field-dependent massive gravity model that remains ghost-free and explores its potential cosmological implications, including a scenario where the graviton mass evolution drives cosmic acceleration.

Contribution

It proposes a new mass-varying massive gravity model with a scalar field, demonstrating its ghost-free nature and analyzing its cosmological evolution.

Findings

The model is free of the Boulware-Deser ghost.

The scalar field can drive cosmic acceleration.

Graviton mass evolves from high to low energy scales.

Abstract

It has recently been shown that the graviton can consistently gain a constant mass without introducing the Boulware-Deser ghost. We propose a gravity model where the graviton mass is set by a scalar field and prove that this model is free of the Boulware-Deser ghost by analyzing its constraint system and showing that two constraints arise. We also initiate the study of the model's cosmic background evolution and tentatively discuss possible cosmological implications of this model. In particular, we consider a simple scenario where the scalar field setting the graviton mass is identified with the inflaton and the graviton mass evolves from a high to a low energy scale, giving rise to the current cosmic acceleration.