Viability of bigravity cosmology
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 nonlinear scalar self-interactions conspire to reproduce general relativity 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 Vainshtein mechanism. We find that the requirement of having a successful Vainshtein mechanism is not compatible with the existence of cosmological solutions at early times.