Abstract
We study the generation of neutrino masses in the SU(3) W electroweak unified theory in M 4 x S 1 /(Z 2 x Z 2 ′) spacetime. By appropriate orbifolding, the bulk symmetry SU(3) W is broken into SU(2) L x U(1) Y at one of the fixed points, where the quarks reside. The leptons form SU(3) W triplets, localized at the other symmetric fixed point. The fermion masses arise from the bulk Higgs sector containing a triplet and an anti-sextet. We construct neutrino Majorana masses via 1-loop quantum corrections by adding a parity odd bulk triplet scalar. No right-handed neutrino is needed. The neutrino mass matrix is of the inverted hierarchy type. We show that the model can easily accommodate the bi-large mixing angle solution favored by the recent neutrino experiments without much fine tuning of parameters. The constraints from μ → 3e transition and neutrinoless double β decays are discussed. Crown copyright © 2003 Published by Elsevier Science B.V. All rights reserved.