Institute for Advanced Study Astrophysics Seminar

Theories that attempt to explain the observed cosmic acceleration generally introduce new degrees of freedom (such as a scalar) that are active on large scales but must be screened on small scales. We show that O(1) equivalence principle violations are expected if the screening mechanism is chameleon or symmetron, while such violations are O(v/c)2 suppressed if the screening mechanism is Vainshtein. This violation of equivalence principle occurs despite a universal scalar-matter coupling, and is the result of a classical renormalization of the scalar charge for a macroscopic object. Observational tests will be discussed.