NEUTRINO MASSES, MAGNETIC-MOMENTS, AND HORIZONTAL SYMMETRIES

We investigate the general structure of the neutrino mass and magnetic moment matrices in the presence of an unbroken horizontal symmetry. In particular, we study the compatibility of masslessness induced by such a symmetry and a non-zero magnetic moment. We show that in this case at least two of the charged leptons must have equal masses. Furthermore, we give a general definition of Dirac neutrinos and demonstrate that they are not necessarily associated with a lepton number.