Neutrino masses in the $SU(4)_L \otimes U(1)_X$ electroweak extension of   the standard model
  We study the neutrino mass generation in the $SU(4)_L \otimes U(1)_X$ electroweak extension of the standard model by considering non-renormalizable dimension five effective operators. It is shown that there exist two topologies for the realizations of such an operator at the tree-level and for one of the three-family models is explore the neutrino phenomenology after extending its particle content with an $SU(4)_L$ fermion singlet and a scalar decuplet. Constraints in the available parameters space of the model are partially discussed. 
Guillermo Palacio
hep-ph