Lorentz-Violating Massive Gravity in Curved Space

TL;DR

This paper introduces a Lorentz-violating massive gravity model in curved space that modifies general relativity without adding instabilities or extra propagating modes, affecting cosmological evolution in the infrared regime.

Contribution

It presents a novel Lorentz-violating potential for gravity that avoids extra degrees of freedom and classical instabilities, with implications for cosmological bounce scenarios.

Findings

No additional propagating modes or classical instabilities.

Model modifies GR only in the infrared regime.

Cosmological evolution includes a bounce at large scales.

Abstract

In models of modified gravity, extra degrees of freedom usually appear. They must be removed from the spectrum because they may indicate the presence of instabilities and because otherwise the model might not agree with observation. In the present letter, we will discuss a model that modifies General Relativity through the addition of a Lorentz-violating potential-like term for the metric. No additional propagating modes and no classical instabilities are present. The model departs from GR only in the extreme infrared region, and the cosmological evolution contains a bounce when the size of the Universe is of the same order of the added deformation.