###### "Equivalence Principle on Cosmological Backgrounds in Scalar-Tensor Theories"

We study the extent up to which the equivalence principle is obeyed in models of modified gravity and dark energy involving a single scalar degree of freedom. In particular, we focus on the so-called effective field theories of dark energy. We show that in the case of an exactly de Sitter universe both the weak and strong equivalence principles hold. When generalized to Friedmann--Robertson--Walker cosmologies (FRW) we show that the weak equivalence principle is obeyed for test particles and extended objects in the quasi-static subhorizon limit. We do this by studying the field created by an extended object moving in an FRW background as well as its equation of motion in an external gravitational field.

**About the speaker**

Lasma Alberte is a Research Associate at Imperial College, London. Lasma's research interests include: modified gravity, holographic massive gravity, cosmology, and effective field theories.