# On the viability of bigravity cosmology

## TL;DR

This paper assesses the potential of bigravity cosmology as a dark energy model by analyzing linear and non-linear perturbations, revealing tensions between local gravity recovery and early universe solutions.

## Contribution

It provides a detailed perturbation analysis of bigravity cosmology, identifying parameter constraints for viability and highlighting conflicts between local and early universe behaviors.

## Key findings

- Vainshtein mechanism can recover GR on small scales
- Parameter space for late-time acceleration is constrained
- Early universe solutions conflict with Vainshtein mechanism requirements

## Abstract

We revisit the question of viability of bigravity cosmology as a candidate for dark energy. In the context of the low energy limit model, where matter couples to a single metric, we study linear perturbations around homogeneous and isotropic backgrounds to derive the Poisson's equation for the Newtonian potential. Extending to second order perturbations, we identify the Vainshtein radius below which non-linear scalar self interactions conspire to reproduce GR on local scales. We combine all of these results to determine the parameter space that allows a late time de-Sitter attractor compatible with observations and a successful Vainsthein mechanism. We find that the requirement on having a successful Vainsthein mechanism is not compatible with the existence of cosmological solutions at early times.