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Global fits of axions and WIMPs in astrophysics, cosmology, and particle physics

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Title: Global fits of axions and WIMPs in astrophysics, cosmology, and particle physics
Authors: Hoof, Sebastian
Item Type: Thesis or dissertation
Abstract: I present my contributions towards constraining dark matter candidates with global statistical analyses. In particular, I show results for global fits of axion models and for gamma ray searches in dwarf spheroidal galaxies, looking for weakly interacting massive particles. For the former, I consider the scenario where the Peccei-Quinn symmetry breaks before the end of inflation and the axion’s initial field value is a random variable. I combine experimental results from astrophysics, cosmology, and laboratory experiments to yield the most statistically rigorous constraints on these models to date. This includes Bayesian and frequentist exclusion regions for the various parameters and models while also considering the effect of the potentially anomalous cooling in white dwarfs. Using Bayesian techniques, it is possible to make statements about the parameters and abundance of axions in this Peccei-Quinn symmetry breaking scenario. As a result, axions probably make up a sizeable fraction – but not the majority – of dark matter. I then revisit different sources of uncertainties on the axion realignment density, estimating the statistical ones with analytical approximations. Finally, I combine gamma ray data from 27 dwarf spheroidal galaxies to place limits on the dark matter annihilation into Standard Model particles. The analysis carefully includes the uncertainties on the dwarfs’ dark matter content. The resulting constraints on the cross section are similar to previous analyses for higher masses, while they are stronger for lower masses. As a consequence, some of the remaining dark matter explanations of the Galactic Centre excess can be ruled out.
Content Version: Open Access
Issue Date: May-2019
Date Awarded: Dec-2019
URI: http://hdl.handle.net/10044/1/76506
DOI: https://doi.org/10.25560/76506
Copyright Statement: Creative Commons Attribution NonCommercial Licence
Supervisor: Scott, Pat
Trotta, Roberto
Sponsor/Funder: Imperial College London
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses