SEESAW MAJORON MODEL OF NEUTRINO MASS AND NOVEL SIGNALS IN HIGGS-BOSON PRODUCTION AT LEP

We perform a careful study of the neutral scalar sector of a model whi ch includes a singlet, a doublet, and a triplet scalar field under SU( 2), This model is motivated by neutrino physics, since it is simply th e most general version of the seesaw model of neutrino mass generation through spontaneous violation of lepton number. The neutral Higgs sec tor contains three CP-even and one massive CP-odd Higgs boson A, in ad dition to the massless CP-odd majoron J. The weakly interacting majoro n remains massless if the breaking of lepton number symmetry is purely spontaneous. We show that the massive CP-odd Higgs boson may invisibl y decay to three majorons, as well as to a CP-even Higgs H boson plus a majoron. We consider the associated Higgs production e(+)e(-) --> Z --> HA followed by invisible decays A --> JJJ and H --> JJ and derive the corresponding limits on masses and coupling that follow from LEP I precision measurements of the invisible Z width. We also study a nove l b (b) over bar b (b) over bar p(T) signal predicted by the model, an alyze the background and perform a Monte Carlo simulation of the signa l in order to illustrate the limits on Higgs boson mass, couplings and branching ratios that follow from that. (C) 1998 Elsevier Science B.V .