Fermion Masses and Mixing in 331 Models with Horizontal Symmetry
  The possibility of adding an SU(2) horizontal symmetry to the 331 model is studied. It is found that simple, anomaly-free fermion assignments can be made which lead to plausible results for fermion masses and mixings. In particular, all particles of the first generation are massless at tree-level, and the CKM matrix acquires a realistic form. 
M. B. Tully and G. C. Joshi (University of Melbourne)