In this thesis we analyze the importance of the one-loop corrections and
the non-perturbative Sommerfeld enhancement on the dark matter thermal
relic density and indirect detection signals. We discuss general properties
of these e ects and present a detailed study of their impact in the Minimal
Supersymmetric Standard Model. For the Sommerfeld e ect (SE) we have developed a general formalism to compute the enhancement factors for a multi-state system of fermions, in all possible spin con gurations and with generic long-range interactions. We show how to include such SE e ects in an accurate calculation of the thermal relic density for WIMP dark matter candidates. We apply the method to the MSSM and perform a numerical study of the relic abundance of neutralinos with arbitrary composition and including the SE due to the exchange of the W and Z bosons, photons and Higgses. Additionally, we perform an analogous
analysis in the case of large co-annihilation e ects with a scalar particle,
presenting also the appropriate formulas for a general scenario of this kind, with a set of particles with arbitrary masses and (o -)diagonal interactions. We nd non-negligible corrections in whole sfermion co-annihilation regimes and a very strong e ect for the heavy Wino-like neutralino. We also provide a numerical package for computing the neutralino relic density including the Sommerfeld e ect in a general MSSM setup. We turn then to a speci c scenario, where the dark matter is made of Winolike particles, and study the indirect detection signals including both our full computation of one-loop level electroweak corrections and the Sommerfeld e ect. We discuss how to incorporate them simultaneously and present the results for the full present-day annihilation cross-section. Having well under control the particle physics properties of the model, we concentrate on what exclusion limits and detection prospects we can obtain for this model taking into account various astrophysical uncertainties. Our results on the indirect detection signals show a signi cant impact of higher order e ects and moreover the importance of cross correlation between various search channels.
