Phenomenological and theoretical aspects of low energy scale type II seesaw mechanism

Abstract

The Standard Model (SM) of Particle Physics provides the most accurate description of the behaviour of matter in the smallest accessible distance scales. However, since it does not account for the nonzero neutrino masses and it is also plagued with a number of theoretical, experimental and cosmological issues, it is widely accepted that the SM must be extended. Besides, there are three canonical mechanisms that elucidate naturally neutrino mass smallness at tree-level. Among them, the most versatile one is type II seesaw (in this thesis we will explain why). A simple realization of this mechanism extends SM by a scalar triplet with hypercharge that interacts with leptonic doublets, known as Higgs Triplet Model (HTM). After spontaneous symmetry breaking (SSB), left-handed neutrinos gain masses. As any other seesaw, it has a term that violates lepton number by two units and the energy scale in which this violation occur tell us how heavy are such new scalars. For example, if lepton number is explicitly broken at low energies, the scalar triplet components acquire masses near to TeV scales. Thus, it is tempting to study such phenomenological viable model and its consequences in actual colliders, since it is not settled if there is only the SM Higgs boson or a more complex scalar scheme. We discuss several aspects of HTM, highlighting phenomenological implications in each case. In particular, we searched in detail for new LFV processes, diphoton decay of the new Higgs boson, decay of the doubly-charged scalar and contribution of such extension to the e− scattering process. We also discuss about the stability of the Higgs potential. We argue about the possibility to the Higgs vacuum becomes stable in a more complex model and under what configuration of parametric space such model must obey to ensure stability.