Cosmological constraints on massive gravity

As discussed in the previous talk, a promising approach to explain the current accelerated expansion of the Universe is to extend general relativity to include a non-zero graviton mass. The resulting modification is expected to lead to different background expansion and growth of structure compared to the standard cosmological constant with cold dark matter model. In this talk, I will present results on the growth of matter perturbations in a quasidilaton extension of the de Rham-Gabadadze-Tolley (dRGT) theory of massive gravity, that allows for a stable cosmology. Starting in conformal Newtonian gauge, where scalar perturbations coincide with gauge-invariant ones, I will first obtain coupled differential equations in all propagating degrees of freedom. I will next discuss two sub-horizon approximations that allow us to find a single equation describing the growth of matter perturbations and show how the resulting growth of structure compares to the standard cosmological model. Lastly, I will discuss the constraints on various model parameters, including the mass of the graviton, from a Markov-Chain Monte-Carlo analysis that compares the background evolution to supernovae data and the growth of perturbations to galaxy clustering data.