Cosmic expansion histories in massive bigravity with symmetric matter coupling

TL;DR

This paper investigates the cosmic expansion in massive bigravity with symmetric matter coupling, deriving the Friedmann equation and exploring models that replicate or extend LCDM cosmology, including dynamical dark energy scenarios.

Contribution

It introduces a viable symmetric matter coupling in massive bigravity and analyzes its implications for cosmic expansion, including specific models like partially-massless theories.

Findings

Background cosmology can match LCDM for certain parameters.

More general parameters produce dynamical dark energy consistent with observations.

Exploration of minimal, maximally-symmetric, and partially-massless models.

Abstract

We study the cosmic expansion history of massive bigravity with a viable matter coupling which treats both metrics on equal footing. We derive the Friedmann equation for the effective metric through which matter couples to the two metrics, and study its solutions. For certain parameter choices, the background cosmology is identical to that of LCDM. More general parameters yield dynamical dark energy, which can still be in agreement with observations of the expansion history. We study specific parameter choices of interest, including minimal models, maximally-symmetric models, and a candidate partially-massless theory.