Abstract

We have great certainty on how gravity works around our solar system: General Relativity (GR) has been found to be very accurate at these small scales. On large scales though, the LCDM model is in good agreement with cosmological data, but relies on the presence of several unknown components, whose origin and nature are not yet understood. For this reason, it is important to test the validity of GR on cosmological scales.

In this talk I will show a method to parametrise deviations from GR at large scales. Ultimately, the objective is to use experimental data to constrain the free parameters in the model and, as result, test GR and identify possible viable modifications that will help us understand better gravity in this regime. The method I will show is general and systematic, and allow us to construct the most general quadratic action for linear cosmological perturbations, given some field content and gauge symmetries. It is possible to apply the method to obtain parametrised cosmological models that encompass classes of gravity theories, such as scalar-tensor, vector-tensor and bimetric theories.