Infrared-modified gravities and massive gravitons

TL;DR

This paper reviews various theoretical and phenomenological aspects of massive gravity theories in four dimensions, focusing on Lorentz-invariant and Lorentz-violating models, highlighting their differences and potential physical implications.

Contribution

It provides a comparative analysis of Lorentz-invariant and Lorentz-violating massive gravity models, emphasizing the absence of pathologies in certain Lorentz-violating theories.

Findings

Lorentz-violating models can avoid spectrum pathologies

Some models exhibit interesting phenomenology

Lorentz-invariant models have spectrum issues

Abstract

We review some theoretical and phenomenological aspects of massive gravities in 4 dimensions. We start from the Fierz--Pauli theory with Lorentz-invariant mass terms and then proceed to Lorentz-violating masses. Unlike the former theory, some models with Lorentz-violation have no pathologies in the spectrum in flat and nearly flat backgrounds and lead to interesting phenomenology.