## Séminaire de Physique Théorique

**Dark energy: an effective field theory approach**

Federico Piazza (Paris 7)

Thursday 24 January 2013 14:00 - Tours - Salle 1180 (Bât E2)

**Résumé :**

The discovery of the accelerating expansion of the Universe is triggering an impressive amount of theoretical and observational activity. After briefly reviewing the problems and challenges of ``Dark Energy", I will focus on recent and ongoing works in which my collaborators and I propose a unifying description of dark energy and modified gravity models that makes use of effective field theory (EFT) techniques. EFT allows to isolate the relevant low energy degrees of freedom and to efficiently study their dynamics. By extending the ``Effective field theory (EFT) of inflation" formalism to late time cosmology, we write the most general action for cosmological perturbations in the presence of an additional scalar degree of freedom. As we argue, in fact, cosmological perturbations are the relevant low energy degrees of freedom in a cosmological set-up. I will focus on a few operators that are quadratic in the perturbations and which appear in non-minimally coupled scalar-tensor gravity and ``Galileon" theories and I will describe the mixing between gravity and the scalar degree of freedom that such operators produce.

**Liens :**