Type II seesaw and a gauge model for the bimaximal mixing explanation of neutrino puzzles

We present an extension of the standard model where the bimaximal mixing pa ttern among the neutrinos naturally arises via the type II seesaw mechanism . This explains both the atmospheric and solar neutrino data via large angl e vacuum oscillation among the three known neutrinos. The model does not in clude righthanded neutrinos but additional Higgs triplets which acquire nat urally small vev's due to the type II seesaw mechanism. The presence of a g lobal L-e - L-mu - L-tau and S-3 symmetry leads naturally to the desired ma ss splittings among neutrinos at the one loop level. This model predicts ob servable branching ratios for tau --> mu mu mu, which could be used to test the model. (C) 2000 Published by Elsevier Science B.V. All rights reserved .