The idea of quark-lepton universality at high energies has recently been explored in unified theories based upon the quartification gauge group $SU(3{)}^4$. These schemes encompass a quark-lepton exchange symmetry that results upon the introduction of leptonic color. It has been demonstrated that, in models in which the quartification gauge symmetry is broken down to the standard model gauge group, gauge coupling constant unification can be achieved, and there is no unique scenario. The same is also true when the leptonic color gauge group is only partially broken, leaving a remnant $SU(2{)}_{\ell }$ symmetry at the standard model level. Here we perform an analysis of the neutrino mass spectrum of such models. We show that these models do not naturally generate small Majorana neutrino masses, thus correcting an error in our earlier quartification paper, but with the addition of one singlet neutral fermion per family there is a realization of seesaw suppressed masses for the neutrinos. We also show that these schemes are consistent with proton decay.

• Received 23 March 2006

DOI:https://doi.org/10.1103/PhysRevD.74.033005