Detecting Chameleon Dark Energy via Electrostatic Analogy
Jones-Smith, Katherine (Washington University in St Louis)

In recent years, scalar-tensor modifications of gravity have become a prominent alternative to the cosmological constant as the cause of cosmic acceleration. In such models, scalar fields couple to matter with gravitational strength or greater--naively one would expect such strongly coupled fields to interfere with precision tests of gravity but \\\\\\\"screening mechanisms\\\\\\\" can provide recourse. One screening mechanism of great interest is the thin shell suppression effect, wherein the scalar field forms very thin shell just under the surface of a dense body. This was first described in the context of chameleon models of dark energy, but the thin shell effect also appears in symmetron models, and plays a central role in viable f(R) theories. \\\\r\\\\n We present an analogy between scalar fields in the thin shell regime and electrostatics, which follows from noting that the same equations govern both the electrostatic potential and the chameleon field in the thin shell regime. This analogy enriches our understanding of the thin shell screening and enables us to solve for the chameleon profile in geometries other than the spherically symmetric ones typically assumed. We find that the chameleon field is enhanced towards the end of a pointed or elongated object-- a lightning rod style effect that could be used to leverage the thin shell suppression. We also find that an elongated object such as an ellipsoid would experience a torque in the presence of a chameleon field with a uniform gradient, and that the magnitude of the torque is comprable to the sensitivity of existing experiments. This novel effect could be used to unveil the presence of a screened scalar field, even in the experimentally unfavorable thin shell regime.