Cosmology of the Galileon from Massive Gravity

TL;DR

This paper studies a covariantized version of massive gravity's decoupling limit, revealing a self-accelerating cosmological solution, stability conditions, and effects on structure formation, highlighting the importance of frame choice in proxy theories.

Contribution

It introduces a covariant proxy for massive gravity's decoupling limit and analyzes its cosmological solutions, stability, and implications for structure formation.

Findings

Existence of a self-accelerating solution with Hubble parameter equal to graviton mass

Stable fluctuations around the self-accelerating background for certain parameters

Helicity-0 mode enhances structure formation relative to LCDM

Abstract

We covariantize the decoupling limit of massive gravity proposed in arXiv:1011.1232 and study the cosmology of this theory as a proxy, which embodies key features of the fully non-linear covariant theory. We first confirm that it exhibits a self-accelerating solution, similar to what has been found in arXiv:1010.1780, where the Hubble parameter corresponds to the graviton mass. For a certain range of parameters fluctuations relative to the self-accelerating background are stable and form an attractor solution. We also show that a degravitating solution can not be constructed in this covariantized proxy theory in a meaningful way. As for cosmic structure formation, we find that the helicity-0 mode of the graviton causes an enhancement relative to LCDM. For consistency we also compare proxy theories obtained starting from different frames in the decoupling limit and discuss the possibility of obtaining a non-representative proxy theory by choosing the wrong starting frame.