Naturally light right-handed neutrinos in a 3-3-1 Model
  In this work we show that light right-handed neutrinos, with mass in the sub-eV scale, is a natural outcome in a 3-3-1 model. By considering effective dimension five operators, the model predicts three light right-handed neutrinos, weakly mixed with the left-handed ones. We show also that the model is able to explain the LSND experiment and still be in agreement with solar and atmospheric data for neutrino oscillation. 
Alex G. Dias, C. A. de S. Pires, P. S. Rodrigues da Silva