Testing a specific Generalized Brans-Dicke model with the unified Effective Field Theory approach.

One of the most intriguing puzzle of modern Cosmology resides in the late time accelerated expansion of our Universe. Our standard model of Cosmology, the LCDM model, based on the General Relativity theory of gravity, explains this phenomenon in terms of a cosmological constant added into the Einstein equations. Despite the successful agreement of the LCDM model with cosmological data, some issues and internal inconsistencies are still without a satisfactory explanation. This motivates the quest for alternative cosmological model and the necessity of probing gravity at cosmic scales. This Master Thesis is about studying a specific modified gravity model, dubbed as Generalized Brans-Dicke theory, employing the unified language offered by the Effective Field Theory approach to dark energy. Implementing the Generalized Brans-Dicke theory in the EFTCAMB cosmological code, we study the model from a phenomenological point of view. We focus in particular on stability criteria, cosmological perturbations and we perform a Monte Carlo Markov Chain likelihood analysis to estimate parameters using recent cosmological datasets.