Dissertation

Dark Matter Genesis

Kirk, Russell

2017

Overview

There is abundant evidence pointing to an unseen component of the Universe comprising approximately 80% of its mass; this dark matter cannot be any known particle, and so demands new physics. Very little is known about dark matter, however from the cosmic microwave background, its abundance has been accurately measured. How this is produced then dictates the requirements placed on a theory of dark matter. Here four works [1-4] are described where theories of dark matter genesis are explored. The first mechanism considers an additional source of dark matter from decaying topological defects in the early Universe. Topological defects are massive structures formed during spontaneous symmetry breaking phase transitions, which evolve under their own tension and decay, possibly producing dark matter during freeze-out. This allows the annihilation cross-section to rise above what is required in standard freeze-out, as the losses in abundance it predicts, may be recuperated by the contributions from the decaying defects. Given this, the constraints standard freeze-out imposes on dark matter models can be loosen. This is illustrated by implementing the mechanism in an example theory, the Inert Doublet Model, where it opens up large swathes of parameter space and allows for lighter dark matter masses. Furthermore this mechanism is employed to resolve issues with dark matter interpretations of the galactic centre gamma-ray excess seen by Fermi-LAT. The cross-section required to produce this signal is in tension with limits from searches in dwarf spheroidal satellite galaxies. Using this mechanism in a p-wave annihilating model of dark matter, this tension is avoided while producing the correct relic abundance of dark matter. Additionally we examine the direct detection signatures in upcoming detectors, DEAP-3600 and XENON1T, of nuclear dark matter: bound states of strongly-interacting dark nucleons, formed during a synthesis period in the early Universe. Scatterings of states in this model produce characteristic recoil spectra, which we found can be distinguished to 3 sigma confidence level from WIMP spectra with as few as ~24 events. Subsequently there is potential for discovery in the not too distant future.

• Publisher: ProQuest Dissertations & Theses
• Subject: Big Bang theory / Dark matter / Phase transitions