Phenomenology of the neutrino-mass-giving Higgs triplet and the low-energy seesaw violation of lepton number

Small realistic Majorana. neutrino masses can be generated via a Higgs triplet (xi (++), xi (+), xi (0)) without having energy scales larger than M-* = O (1) TeV in the theory. The large effective mass scale A in the well-known seesaw neutrino-mass operator Lambda (-1) (LL Phi Phi) is naturally obtained with Lambda similar to M-*(2)/mu where It is a small scale of lepton-number violation. In theories with large extra dimensions, the smallness of mu is naturally obtained by the mechanism of shining if the number of extra dimensions n greater than or equal to 3. We study here the lEggs phenomenology of this model, where the spontaneous violation of lepton number is treated as an external source from extra dimensions. The observable decays xi (++) --> l(i)(+)l(j)(+) will determine directly the magnitudes of the (ij) elements of the neutrino mass matrix. The decays xi (+) --> W(+)J(0) and xi (0) --> ZJ(0), where J(0) is the massless Goldstone boson (Majoron), are also possible, but of special importance is the decay xi (0) --> J(0)J(0) which provides stringent constraints on the allowed parameter space of this model. Based on the current neutrino data, we also predict observable rates of mu -e conversion in nuclei. (C) 2001 Elsevier Science B.V. All rights reserved.