Detecting solar chameleons through radiation pressure

Abstract

Light scalar elds can drive the accelerated expansion of the universe. Hence, they are obvious dark energy candidates. To make such models compatible with tests of General Relativity in the solar system and \fth force" searches on Earth, one needs to screen them. One possibility is the so-called \chameleon" mechanism, which renders an eective mass depending on the local matter density. If chameleon particles exist, they can be produced in the sun and detected on Earth exploiting the equivalent of a radiation pressure. Since their eective mass scales with the local matter density, chameleons can be re ected by a dense medium if their eective mass becomes greater than their total energy. Thus, under appropriate conditions, a ux of solar chameleons may be sensed by detecting the total instantaneous momentum transferred to a suitable opto-mechanical force/pressure sensor. We calculate the solar chameleon spectrum and the reach in the chameleon parameter space of an experiment using the preliminary results from a force/pressure sensor, currently under development at INFN Trieste, to be mounted in the focal plane of one of the X-Ray telescopes of the CAST experiment at CERN. We show, that such an experiment signies a pioneering eort probing uncharted chameleon parameter space.