$SU(4)_L \otimes U(1)_N$ model for the electroweak interactions
  Assuming the existence of right-handed neutrinos, we consider an electroweak model based on the gauge symmetry $SU(4)_L\otimes U(1)_N$. We study the neutral currents coupled to all neutral vector bosons present in the theory. There are no flavor changing neutral currents at tree level, coupled with the lightest neutral vector boson. 
F. Pisano and V. Pleitez