Gauged B-3L_\tau, low-energy unification and proton decay

We point out that if there is a gauged $B-3L_{\tau }$ symmetry at low energy, it can prevent fast proton decay. This may help building models with theories with extra dimensions at the TeV scale. For purpose of illustration we present an explicit model with large extra dimensions. The Higgs required for a realistic fermion masses and mixing are included. The problem of neutrino masses are solved with triplet Higgs scalars. The proton remains stable even after the $B-3L_{\tau }$ symmetry breaking.