Constraining the chameleon-photon coupling with atomic spectroscopy

Abstract

We compute bounds from atomic spectroscopy on chameleon fields that couple to the photon. Chameleons are a wide class of scalar field models that generically lead to screened fifth forces and a host of novel phenomenologies, particularly when the photon coupling is included. We account for perturbations to the atomic energy levels from both the scalar field ‘fifth force’ and the scalar field’s correction to the electric field. We also account for the electromagnetic interaction’s contribution to the scalar charge of the proton, which enables a considerably wider class of models to be tested than without this effect. We find bounds that cover different areas of chameleon parameter space. A range of models spanning approximately one order of magnitude in chameleon coupling parameters (around M,Mγ≈10−16MPl) are excluded for the first time. We also show that improvements to the theoretical uncertainty of hydrogen’s spectrum within the Standard Model would immediately rule out additional chameleon theory space by this analysis. Published by the American Physical Society 2024