title: Violation of the equivalence principle in modified theories of gravity.
abstract: We show that the metric in f(R) theories of gravity in Palatini formalism can be solved as the product of a rank-two tensor times a scalar function which is very sensitive to the local energy-momentum densities. This local dependence of the metric generates new gravitationally-induced microscopic interactions, which eventually would lead to self-accelerated test body trajectories. These facts make very unlikely the viability of Palatini f(R) models designed to change the late-time cosmic evolution.
authors.affiliation: Physics Department, University of Wisconsin-Milwaukee, Post Office Box 413, Milwaukee, Wisconsin 53201, USA.
authors.forename: Gonzalo J
authors.initials: GJ
authors.lastname: Olmo