Neutrinos massivos e mecanismo de geração de massa em uma extensão abeliana do modelo padrão

Abstract

Neutrino oscillation is a quantum phenomenon where these particles alternate between their flavor states: νe,νµ,ντ. These oscillations, as is known by experiment, are caused by the existence of massive neutrino states. In the Standard Model of Particle Physics (SM), the neutrino is a particle with no electric charge, no color charge and no mass, interacting only weakly. With the discovery of oscillations and, consequently, of the massive states of neutrinos, there was a need to postulate mechanisms of mass generation beyond the Higgs Mechanism, which is the standard mechanism in the SM. The type 1 seesaw mechanism postulates that a mass term for neutrinos can be generated by the exchange of virtual heavy leptons between the parties involved (the Higgs and leptons doublets). This work presents a brief review of the history of neutrinos, commenting on the main experimental results up to the discovery of the Tau neutrino, ντ. Then there is an exposition of the theory of free fields of spins 0, 1/2 , and 1. Then we write about the most relevant interactions for our case: the electroweak theory for leptons and the mechanism of Higgs. Once this is done, we begin the theory of massive neutrinos with special attention to mixing and oscillations in the vacuum. We will do a study of two types of mass terms for neutrinos: the Dirac case and the Majorana case. Next, we will write about the type 1 seesaw mechanism, where we write the Weinberg Effective Lagrangian and diagonalize the seesaw matrix. On the final chapter we will approach a mechanism of mass generation for neutrinos in the scenario of an abelian extension of the SM. These extensions bring new fields and a new set of charges to the SM. In this scenario we will show that we can construct an effective operator that, after symmetry breaking, generates Dirac mass terms for neutrinos.