Generation of small neutrino Majorana masses in a Randall-Sundrum model

Abstract

I propose a model, in the framework of five dimensions with warped geometry, in which small neutrino Majorana masses are generated by tree-level coupling of lepton doublets to a $SU(2{)}_{L}$-triplet scalar field, which is coupled to a bulk standard model singlet. The neutrino mass scale is determined by the bulk mass term $({\ensuremath{\alpha}}_{S})$ of the singlet as $v{e}^{\ensuremath{-}2({\ensuremath{\alpha}}_{S}\ensuremath{-}1)\ensuremath{\pi}kR}$. This suppression is due to a small overlap between the profile of the singlet zero mode and the triplet, which is confined to the TeV brane. The generic form for the neutrino mass matrix due to the overlap between the fermions is not compatible with the large mixing angle solution. This is overcome by imposing a ${Z}_{4}$ symmetry, which is softly broken by couplings of the triplet Higgs to the lepton doublets. This model successfully reproduces the observed masses and mixing angles in the charged lepton sector as well as in the neutrino sector, in addition to having a prediction of $|{U}_{e3}|\ensuremath{\sim}\mathcal{O}(0.01)$. The mass of the triplet is of the order of a TeV and could be produced at upcoming collider experiments. The doubly charged member of the triplet can decay into two same sign charged leptons, yielding the whole triplet coupling matrix which, in turn, gives the mixing matrix in the neutrino sector.