Gauged $B - 3 L_\tau$ and Baryogenesis
  It has recently been shown that by extending the minimal standard model to include a right-handed partner to $\nu_\tau$, it is possible to gauge the $B - 3 L_\tau$ quantum number consistently. If we add two scalar triplets, one trivial ($\xi_1$) and one nontrivial ($\xi_2$) under $B - 3 L_\tau$, it is possible also to have desirable neutrino masses and mixing for neutrino oscillations. At the same time, a lepton asymmetry can be generated in the early universe through the novel mechanism of the decay of the heavier $\xi_1$ into the lighter $\xi_2$ plus a neutral singlet ($\zeta^0$). This lepton asymmetry then gets converted into a baryon asymmetry at the electroweak phase transition. 
Ernest Ma and Utpal Sarkar