Chiral effective theory of spin 1 dark matter direct detection

Examensarbete för masterexamen
Ernbrink, Henric
Dark matter (DM) is the collective name for the additional mass needed to explain the data collected from a very wide range of different astronomical observations. Everything from the velocity dispersion of galaxies, gravitational lensing caused by galaxies, the large scale structure of the universe as well as the structure of the microwave background radiation all indicate the existence of DM. The exact nature of DM is however still unknown, but it is largely believed to be new fundamental particle, outside of the current standard model of particle physics. The elusiveness of DM is largely due to the fact that the effects of DM never have been observed at microscopic scales. One promising method for detecting DM particles that permeate the galaxy is in so called direct detection experiments, in which, detectors monitor the recoils of nuclei caused by the scattering of DM which is hitting the Earth [1]. The goal with this work is to provide new theoretical insights into the behavior of scattering between DM and nuclei. In this work DM is assumed to be a weakly interacting massive particle (WIMP) and that it is non-relativistic. Further, it is also assumed to have spin 1. The cross section for the scattering of DM against nuclei is calculated using chiral effective theory, which has not been done before for spin 1 DM. This methodology has a substantial advantage over non-relativistic theories where the degrees of freedom are limited to nucleons and DM since it also includes mesons and consequently can model the effect of meson exchange. In this work it is shown that the inclusion of the meson exchange is crucial especially when modeling the scattering of DM with heavier elements, e.g. xenon, which is a common choice in direct detection experiments [2]. It is also shown that the non-relativistic operators that span the possible DM-nucleon interactions generally cannot be studied individually in direct detection. This is due to the fact that the interaction operators in the more general relativistic theory match onto several DM-nucleon interaction operators. Several DM-nucleon interaction operators consequently share common coupling constants and must generally be studied together.
Dark matter, direct detection, spin 1, chiral effective theory, EFT
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