Systematic Study of Fermion Masses and Mixing Angles in Horizontal SU(2)   Gauge Theory
  Despite its great success in explaining the basic interactions of nature, the standard model suffers from an inability to explain the observed masses of the fundamental particles and the weak mixing angles between them. We shall survey a set of possible extensions to the standard model, employing an SU(2) ``horizontal'' gauge symmetry between the particle generations, to see what light they can shed on this problem. 
Donald S. Shaw and Ray R. Volkas