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Abstract

We propose two extensions of the Standard Model which predict Majorana neutrinos: Zee-SU(5) and Zee- LR. In both theories neutrinos get mass at the quantum level through the Zee mechanism. The Zee-SU(5) is based on the SU(5) grand unified theory with 5_H, 45_H and 10_H composing the scalar sector. The role of the second Higgs doublet in the 45_H is crucial since it is responsible of correcting the down-type quarks and charged leptons mass relation and generating neutrino masses. In order to understand the testability of the theory, unification constraints are studied in detail and proton decay bounds are discussed at current and future experiments such as Hyper-Kamiokande. The theory predicts as a natural outcome a beautiful relation between neutrino masses and charged fermion masses and a light colored octet which could give rise to exotic signatures at the LHC. On the other hand, the Zee-LR is a simple left-right symmetric model whose scalar sector is composed of two Higgs doublets, responsible of breaking the left-right symmetry, and one charged singlet, responsible of the neutrino mass generation and lepton number violation processes. This model predicts light sterile neutrinos. In order to understand the testability of the theory, we study the signatures with two charged leptons of different flavor and missing energy at the LHC and the decays of the heavy gauge bosons involving the light right handed neutrino.We remark that both theories have the minimal degrees of freedom in the scalar sector needed for symmetry breaking and mass generation such that the renormalizability of the theory is preserved (without extra fermion singlets in the case of Zee-SU(5)).