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Abstract

The hierarchies and regular patterns that occur in the mass spectrum of fermions remain a puzzling phenomenon that the Standard Model has yet to address. In this thesis, we investigate a mechanism that could explain the mass hierarchy between fermion generations from quantum loop corrections. We propose concrete implementations of this mechanism in models that feature new generations of massive vector-like fermions, leading to a generalized seesaw mechanism for quarks and leptons. In these models, the masses of heavier families emerge from a tree level seesaw, while in contrast, lighter generations obtain masses only through higher order loop corrections. Opposed to previous studies that consider multiple scalar extensions, we realize such scenarios with a minimal scalar content and loop corrections primarily arise from new gauge interactions. For this purpose, we examine Abelian and non-Abelian Standard Model gauge extensions. The first involves an additional local U(1) symmetry, while the second belongs to the class of left-right symmetric models. Our study demonstrates that realistic fermion mass patterns can naturally arise from loop factors and neither strongly hierarchical Yukawa couplings nor new global or discrete symmetries are needed. Moreover, small neutrino masses can be incorporated into the mechanism. Since models that include massive neutrinos often predict neutrino non-standard interactions, probing them is a promising approach to learn more about the mechanism behind neutrino masses. We explore the potential of a future muon collider to test neutrino non-standard interactions and the complementary insights it could provide.