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Abstract

A sterile (right-handed) neutrino with mass of keV scale is known to be a good Warm Dark Matter candidate. It is the main objective of this thesis to study how this possibility could be realized in the context of extensions of the Standard Model gauge group. Having such a setup with an additional symmetry breaking scale between the electroweak and Planck scales, the naïve expectation leads to large thermal overproduction of sterile neutrinos. However, we show that su cient entropy release due to out-of-equilibrium decay of other long-lived right-handed neutrinos is capable to dilute the density of the keV scale sterile neutrinos so that the observed Dark Matter abundance is achieved. The universal requirements that should be satis ed by such gauge extensions of the Standard Model, containing right-handed neutrinos, to be viable models of Warm Dark Matter, are presented. Within this scenario, we discuss the possibility of the type I see-saw mechanism and provide a simple example in the context of a left-right symmetric model.