FRW Cosmology in Ghost Free Massive Gravity

TL;DR

This paper explores homogeneous FRW cosmological solutions within ghost free massive gravity, revealing two solution branches and conditions under which realistic cosmological evolution can occur, including late-time acceleration.

Contribution

It demonstrates that dynamical additional metrics enable viable FRW solutions in ghost free massive gravity, with detailed analysis of solution branches and their cosmological implications.

Findings

Two distinct FRW solution branches identified.

Large xi leads to significant deviations from GR early on.

Small xi results in GR-like evolution with late-time de Sitter attractor.

Abstract

We study FRW homogeneous cosmological solutions in the recently found ghost free massive gravity. In previous works it was shown that when the additional extra metric, needed to generate the mass term, is taken as non-dynamical and flat, no homogeneous FRW cosmology exists. We show that, when the additional metric is a dynamical field, a perfectly safe FRW universe exists. FRW solutions fall in two branches. In the first branch the massive deformation is equivalent to an effectively generated cosmological constant whose scale is determined by the graviton mass. The second branch is quite rich: we have FRW cosmology in the presence of a "gravitational" fluid. The control parameter xi is the ratio of the two conformal factors. When xi is large, generically the cosmological evolution greatly differs from GR at the early time. In the small xi region, the evolution is similar to GR and the universe flows at late time toward an attractor represented by a dS phase.