Proton decay, neutrino oscillations and other consequences from supersymmetric SU(6) with pseudo-Goldstone Higgs

We suggest a new mechanism for naturally suppressing dimension five baryon number violating in supersymmetric SU(5 + N) (N = 0,1,...) GUTs. The mechanism is realized through suppression of qqT type couplings, and is implemented by introducing new 'matter' multiplets belonging to symmetric representations of SU(5 + N), Together with the suppression of nucleon decay, these multiplets also enable one to avoid the unwanted asymptotic mass relations m(s) = m(mu), m(d)/m(s) = m(e)/m(mu). As an example, we consider an SU(6) model with pseudo-Goldstone Higgs. By supplementing the model with an anomalous U(1) flavor symmetry, we also obtain a simple 'all-order' solution of the gauge hierarchy problem and natural explanation of charged fermion mass hierarchies and values of the CKM matrix elements. The proton life time tau(p) similar to 10(2)tau(p)(SU(5)) yr. is compatible with experiments, with the dominant decay being p --> Kv(mu,tau). Thanks to the SU(6) symmetry, successful unification of the gauge couplings can be retained, and the value of the strong coupling alpha(s)(M-Z) can be reduced to similar or equal to 0.12. Finally, we show how to accommodate the solar and atmospheric neutrino data through the bi-maximal neutrino mixing scenario, with maximal vacuum v(e) - v(mu,tau) and large angle v(mu) - v(tau) oscillations. (C) 2000 Elsevier Science B.V. All rights reserved.