AbstractThe gravitational evidence for a dark matter component to the Universe comes from a variety of observations across a wide range of scales and epochs. Despite the strong support in favour of its existence, any experiment searching for a non-gravitational signature of dark matter has so far returned a null result. One implication of this is the presence of a huge model space that must still be explored in order to identify and understand dark matter and its properties. This thesis is focused on classifying and con-straining general properties of dark matter, such as its mass or couplings to the Standard Model, from four different angles – cosmology, astrophysics, laboratory experiments and theory. Importantly, considering general properties in this way allows us to better delimit the wide range of options available when constructing dark matter models and searches.
In the context of cosmology, robust lower limits on MeV-scale dark sectors are derived from their impact on Big Bang Nucleosynthesis and the Cosmic Microwave Background. In an astrophysical setting, state-of-the-art Jeans modelling is used to estimate the phase-space distribution of dark matter in dwarf galaxies within the local group. An application of the Pauli principle and Liouville’s theorem then allows us to set a model-independent lower bound on the mass of fermionic dark matter which is complementary to other constraints and competitive with dedicated limits. We also ad-dress the well-known loss of nuclear recoil sensitivity in direct detection experiments to sub-GeV candidates. In particular, we present a new mechanism to generate a boosted local source of dark matter through inelastic cosmic ray collisions in the atmosphere which can lead to more energetic, detectable nuclear recoils. Finally, we explore the theoretical implications of symmetry breaking by gravitational instantons on axion-like theories whose phenomenology relies heavily on the quality of a global symmetry.
|Date of Award
|1 Sept 2021
|Malcolm Fairbairn (Supervisor) & Diego Blas (Supervisor)