Inspecting P-odd, T-odd non-relativistic effective field theory operators for detection of Dark Matter

Abstract

Cosmological observations show that dark matter (DM), which has virtually no electro-magnetic interactions but which is about five times more abundant than familiar "baryonic" matter, must exist. A well-motivated hypothesis postulates the existence of WIMPs (Weakly Interacting Massive Particles) as DM. These particles are thought to interact with (some) known particles with a strength roughly corresponding to the known weak interactions. This renders experimental searches for these particles viable, in particular through elastic scattering on nuclei in a terrestrial detector. For many years, the relevant interaction of WIMPs with protons and neutrons was described by two parameters in each case. These parameters give rise to interactions where the WIMP coupling to the nucleus is independent of nuclear spin and where the WIMP coupling is dependent on nuclear spin. However, it has recently been pointed out, in view of a non-relativistic effective field theory (NREFT) construction, that more than 20 additional parameters could play a role here, which would make interpreting the experimental results significantly more challenging. These additional NREFT parameters describe interactions between WIMP and nuclei which were previously not known. This thesis addresses the question whether the additionally introduced NREFT parameters can play a significant role in describing WIMP-nucleus scattering and which among the additional parameters may be retained along with the traditional approach of using two parameters. In particular, focus herein is directed towards examining such questions for those NREFT parameters which violate discrete symmetries such as Parity (P) and Time Reversal (T). Simplified models, which respect only part of the SM gauge symmetries, have been suggested for generating such P- and T-violating parameters. We have analyzed the interplay of constraints from neutron electric dipole moment (nEDM) searches and direct DM searches for such simplified models. We find that for the majority of scenarios considered, the subleading NREFT parameters can be safely ignored and WIMP-nucleus scattering is sufficiently well described by the older approach of retaining two parameters. This is not surprising since the two parameters are actually zeroth order terms of the NREFT construction and the newly introduced parameters are higher order correction terms. We further identify scenarios where one of the subleading NREFT parameters can be more relevant than the two zeroth order NREFT parameters. Our results provide an improved understanding of the whole set of NREFT parameters and clarify their relevance for analysing experimental searches.