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 $m_s=m_{\mu}$, $\frac{m_d}{m_s}=\frac{m_e}{m_{\mu}}$. As an example, we consider a SU(6) model with pseudo-Goldstone Higgs. By supplementing the model with an anomalous ${\cal U}(1)$ 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 $\tau_p\sim 10^{2}\tau_p^{SU(5)}$~yr. is compatible with experiments, with the dominant decay being $p\to K\nu_{\mu, \tau}$. 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 $\simeq 0.12$. Finally, we show how to accommodate the solar and atmospheric neutrino data through the bi-maximal neutrino mixing scenario, with maximal vacuum $\nu_e-\nu_{\mu, \tau}$ and large angle $\nu_{\mu}-\nu_{\tau}$ oscillations.