ARS leptogenesis in scalar extensions of the standard model

In this thesis, we investigate the possibility of dynamically generating the RHN masses in the context of ARS leptogenesis. Specifically, we extend the type-I seesaw model with two RHNs by introducing a complex scalar singlet Φ and a global U(1)_{B-L} symmetry under which Φ carries charge +2 and the RHNs charge -1. After the spontaneous symmetry breaking (SSB) of U(1)_{B-L}, the real part of Φ acquires a non-vanishing vacuum expectation value, and its coupling to N generates a Majorana massive term for the RHNs. This construction naturally explain the origin of the heavy neutral leptons masses. However, after SSB, two real scalar degrees of freedom remain, Φ and θ (the Majoron), which interact with the RHNs via the Yukawa coupling y_N . These additional interactions may modify the RHNs number density, potentially bringing them into thermal equilibrium before the electroweak phase transition. To take into account this new interaction we first identify the leading contributions, then we modify the Quantum Kinetic Equations to study their effects on the final baryon asymmetry of the universe (BAU). Finally, we perform a parameter scan to explore how the parameter space of viable leptogenesis is modified in this new theoretical framework.