Cosmological perturbations in massive gravity with doubly coupled matter

TL;DR

This paper analyzes the stability of cosmological perturbations in a novel massive gravity theory with a new matter coupling, revealing all five degrees of freedom propagate and establishing parameter constraints for stability.

Contribution

It introduces and studies a new effective matter coupling in massive gravity, demonstrating propagation of all degrees of freedom on FLRW backgrounds and analyzing stability conditions.

Findings

All five degrees of freedom propagate in the new coupling scenario.

Stability conditions impose constraints on the theory's parameters.

The model allows self-accelerating solutions with stable perturbations.

Abstract

We investigate the cosmological perturbations around FLRW solutions to non- linear massive gravity with a new effective coupling to matter proposed recently. Unlike the case with minimal matter coupling, all five degrees of freedom in the gravity sector propagate on generic self-accelerating FLRW backgrounds. We study the stability of the cosmological solutions and put constraints on the parameters of the theory by demanding the correct sign for the kinetic terms for scalar, vector and tensor perturbations.