Neutrino Mass Models with an Abelian Family Symmetry

Abstract

Fermion masses are one of the most fundamental problems of particle physics. While the origin of the observed hierarchy between quark and charged lepton masses remains unexplained in the Standard Model and most of its extensions, the question of whether the neutrinos are massive or not is still open. On the theoretical side, since neutrino masses are not protected by any fundamental symmetry¹, there is no reason to expect them to be zero. Now, if the neutrinos are massive, the rather unnatural suppression of their masses relative to the quarks and charged leptons of the same family has to be explained. On the phenomenological side, massive neutrinos could solve in a natural way several astrophysical and cosmological problems.