Low-energy atomic phenomena: probing fundamental physics and searching for dark matter

Abstract

A huge effort from scientists all around the world has pushed tests of physics to ever higher energy scales (e.g. at CERN), though no trace of non-standard model physics has yet been found. In this thesis, I explore another avenue: the use of high precision atomic physics to study fundamental interactions at low energy. I present new calculations of parity-violating effects in atoms. I consider several approaches, including exploiting the very high accuracy that is possible in simple systems, the very large effects that can be found in more complex systems, and studying processes that are sensitive to hadronic parity violation. Then, I consider the interaction of atoms with various background "cosmic" fields. Candidates for such fields include dark matter (e.g. axions) and physics described by extensions to the standard model. By combining my calculations with existing experimental results, new limits on several parameters of physics beyond the standard model are set. I then consider the specific case of axion dark matter in detail. I calculate several new effects that an axion field would induce in atoms. Crucially, these effects are linear in the axion interaction strength; most current search techniques are based on effects that are at least quadratic in this (extremely small) parameter. Finally, I consider the interaction of WIMPs with electrons in regard to dark matter detection experiments. A very promising claim of a positive detection of WIMPs was made by the DAMA Collaboration. This result is the only long-standing claim for a positive WIMP detection, and electron-interacting WIMPs are the lead candidate. I demonstrate that relativistic effects give the dominant contribution to such processes, meaning that non-relativistic calculations may underestimate the cross section by many orders of magnitude; all previous calculations were performed using non-relativistic wavefunctions. I employ accurate relativistic methods to calculate model-independent cross sections and event rates. By assuming the DAMA signal is due to WIMPs, I calculate the signal that would be expected in another experiment, XENON. By comparing this to the observations of the XENON Collaboration, I entirely rule out electron-interacting WIMPs as the source of the DAMA signal.