Dark Matter Phenomenology in Extensions of the Standard Model
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2016-08
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University of Hawaii at Manoa
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Although there exists gravitational evidence for the existence of dark matter across a wide range of cosmic scales and at many different epochs in cosmic history, confirmed observation of significant dark matter interactions with the Standard Model are ab- sent despite well established theoretical motivations. For example, a stable, thermal, weakly interacting particle with mass around the electroweak scale will, generically, annihilate to the observed relic dark matter density in the early universe. Such particles are commonly predicted by models for new physics proposed to unify Standard Model forces at high scales while managing to control runaway quantum corrections to the Higgs mass. In this thesis, we investigate several different models for dark matter interacting with the Standard Model, along with their respective observational signatures and impacts on cosmology. In the first part, we consider dark matter annihilation as a mechanism for the generation of a lepton asymmetry, which is then converted into a baryon asymmetry via a process known as leptogenisis. In the second part, we investigate constraints on peculiar models of dark matter within the Minimal Supersymmetric Standard Model with a bino-like neutralino Lightest Supersymmeric Particle (LSP). In the third part, we develop constraints on the mass and coupling of a generic species of light dark matter using observations of heavy quarkonium decays at high intensity colliders. We consider a class of leptogenesis models in which the lepton asymmetry arises from dark matter annihilation processes which violate CP and lepton number. Importantly, a necessary one-loop contribution to the annihilation matrix element arises from absorptive final state interactions. We elucidate the relationship between this one-loop contribution and the CP -violating phase. As we show, the branching fraction for dark matter annihilation to leptons may be small in these models, while still generating the necessary asymmetry. We consider a scenario, within the framework of the MSSM, in which dark matter is bino-like and dark matter-nucleon spin-independent scattering occurs via the exchange of light squarks which exhibit left-right mixing. We show that direct detection experiments such as LUX and SuperCDMS will be sensitive to a wide class of such models through spin-independent scattering. Moreover, these models exhibit properties, such as isospin violation, that are not typically observed for the MSSM LSP if scattering occurs primarily through Higgs exchange. The dominant nuclear physics uncertainty is the quark content of the nucleon, particularly the strangeness content. We investigate constraints on the interactions of light dark matter with Standard Model quarks in a framework with effective contact operators mediating the decay of heavy flavor bound state quarkonium to dark matter and a photon. When con- sidered in combination with decays to purely invisible final states, constraints from heavy quarkonium decays at high intensity electron-positron colliders can complement missing energy searches at high energy colliders and provide sensitivity to dark matter masses difficult to probe at direct and indirect detection experiments. We calculate the approximate limits on the branching fraction for Υ(1S) decays to dark matter and a photon. Given the approximate limits on the branching fractions for all dimension 6 or lower contact operators, we present the corresponding limits on the interaction strength for each operator and the inferred limits on dark matter-nucleon scattering. Complementary constraints on dark matter annihilation from gamma-ray searches from dwarf spheroidal galaxies are also considered.
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Physics & Astronomy
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