Growth Histories in Bimetric Massive Gravity

TL;DR

This paper analyzes cosmological perturbations in Hassan-Rosen bimetric gravity, showing how matter and gravitational fluctuations evolve differently from Einstein gravity, especially in quasi-de Sitter regimes.

Contribution

It provides a detailed perturbation analysis in bimetric gravity for general backgrounds, highlighting differences in structure growth compared to Einstein gravity.

Findings

Matter perturbations evolve like in Einstein gravity in de Sitter approximation.

Massive and massless gravitational fluctuations can mix in quasi-de Sitter space.

Growth of structure differs from Einstein gravity in the quasi-de Sitter regime.

Abstract

We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless and massive scalar gravitational fluctuations. Matter perturbations then evolve like in Einstein gravity. We perturb the future de Sitter regime by the ratio of matter to dark energy, producing quasi-de Sitter space. In this more general setting the massive and massless fluctuations mix. We argue that in the quasi-de Sitter regime, the growth of structure in bimetric gravity differs from that of Einstein gravity.