Unveiling chameleon fields in tests of the gravitational inverse-square law

Scalar self-interactions are known to weaken considerably the current constraints on scalar-mediated fifth forces. We consider a scalar field with a quartic self-interaction and gravitation-strength Yukawa couplings to matter particles. After discussing the phenomenology of this scalar field, we assess the ability of ongoing and planned experiments to detect the fifth force mediated by such a field. Assuming that the quartic and matter couplings are of order unity, the current-generation Eöt-Wash experiment at the University of Washington will be able to explore an interesting subset of parameter space. The next-generation Eöt-Wash experiment is expected to be able to detect, or to rule out, the fifth force due to such a scalar with unit quartic and matter couplings at the 3σ confidence level.