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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 5H, 45H and 10H composing the scalar sector. The role
of the second Higgs doublet in the 45H 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)).
