|M.Sc Thesis||Department of Physics|
|Supervisor:||Assoc. Prof. Shadmi Yael|
We study SU(5)X SU(5) GUT models, in which a global triplet symmetry naturally gives both the doublet-triplet splitting and a suppression of triplet couplings to matter. In many models this triplet symmetry is generation-dependent. Fermion masses are then affected both by the triplet symmetry and by the gauge structure. The models are checked for validity based on two criteria. First, we check that the resulting flavor structure is viable. In particular, we show that in some models we can naturally obtain the correct electron-down quark mass ratio, while maintaining Yukawa unification for the second and third generations. Second, we check that baryon and lepton number violating dimension-5 operators are adequately suppressed. We discuss a systematic approach to building models of this kind. As it turns out, the same parameter controls both the flavor hierarchies and the suppression of proton decay. SU(5) X SU(5) models are divided into three classes based on their Higgs representations. It is shown that models of the different classes show qualitativly different flavor physics. Specifically, the models that break the lepton- down sector unification in one generation have leading proton decay amplitudes suppressed by me/md ~ 0.1, while the models that do not, may be valid with leading proton decay amplitudes suppressed further. Finally, we show a model that is ruled out by a combination of constraints from proton decay and flavor physics.