Dark Multiplets

Abstract

In the absence of any hints of new physics in LHC, dark matter candidates interacting through electroweak force are still highly motivated. TeV-scale dark matter is well inspired by notions of naturalness as the new physics is expected to emerge in the TeV regime. In this thesis, we extend the Standard Model by adding an SU(2) DM multiplet in non-chiral representation. The real representations have no coupling to the nuclei at tree level, and survive the direct detection bounds. We showed that the pseudo-real representations can also be viable DM candidates if one includes higher dimensional mass-splitting operators, which avoid the tree-level inelastic scattering through Zboson exchange. Since the masses of gauge mediators are light compared to the dark particles, Sommerfeld effect is dominant and affects the value of annihilation cross-section. We computed the relic abundance through freeze-out mechanism in order to determine DM mass. Gamma ray fluxes in our galaxy and dwarf satellites provide a promising tool to probe EWDM. We confronted the four fermionic representations of the model with the latest astrophysical observations. The effective operators give rise to sizable contributions from Higgs mediated DM interactions with quarks and gluons. A linear combination of the effective couplings λ is identified as the critical parameter in determining the magnitude of the cross-section. When λ is smaller than the critical value, the theory behaves similar to the known renormalisable model, and the scattering rate stays below the experimental reach. Nevertheless, above the criticality, the scattering amplitude of pseudoreal models will be enhanced, so that it would be possible for next generation experiments to probe these multiplets. We studied the parameter space of the theory, considering both indirect astrophysical and direct search constraints. It is inferred that multi-TeV mass scale remains a viable region, quite promising for forthcoming experiments.