New massive bigravity cosmologies with double matter coupling

TL;DR

This paper explores new cosmological solutions in ghost-free massive bigravity with double matter coupling, revealing self-inflated early universes, late-time acceleration, and bouncing cosmologies with unique features.

Contribution

It introduces a novel branch of homogeneous and isotropic solutions in bigravity with double matter coupling, including self-inflated, bouncing, and late-time accelerated cosmologies.

Findings

Discovery of self-inflated FLRW cosmologies during radiation era

Identification of bouncing cosmologies with a non-zero minimum scale factor

Solutions that mimic late-time GR with a cosmological constant

Abstract

We study a previously largely unexplored branch of homogeneous and isotropic background solutions in ghost-free massive bigravity with consistent double matter coupling. For a certain family of parameters we find `self-inflated' FLRW cosmologies, i.e. solutions with an accelerated early-time period during the radiation-dominated era. In addition, these solutions also display an accelerated late-time period closely mimicking GR with a cosmological constant. Interestingly, within this family, the particular case of $\beta_1=\beta_3=0$ gives bouncing cosmologies, where there is an infinite contracting past, a non-zero minimum value of the scale factor at the bounce, and an infinite expanding future.