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Neutrino masses in effective rank-5 subgroups of E-6. I. Nonsupersymmetric case

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2005-06-01
Frank, M
Sher, M
Turan, İsmail
The neutral fermion sectors of E-6-inspired low-energy models, in particular, the alternative left-right and inert models, are considered in detail within the nonsupersymmetric scenario. We show that in their simplest form, these models always predict, for each generation, the lightest neutrino to be a SU(2)(L) singlet, as well as two extra neutrinos with masses of the order of the up-quark mass. In order to recover standard model phenomenology, additional assumptions in the form of discrete symmetries and/or new interactions are needed. These are classified as the discrete symmetry, higher-dimensional operators, and additional neutral fermion methods. The discrete symmetry method can solve the problem, but requires additional Higgs doublets that do not get vacuum expectation values. The higher-dimensional operators method predicts no sterile neutrino, and that the active neutrinos mix with a heavy isodoublet neutrino, thus slightly suppressing the couplings of active neutrinos, with interesting phenomenological implications. The additional neutral fermion method also predicts this suppression, and also naturally includes one or more sterile neutrinos. This scenario allows the existence of sterile neutrino(s) in either a 3+1 or 2+2 structure at low energies, which are favored by the Los Alamos Liquid Scintillation Neutrino Detector result.