Abstract: In left-right symmetric model, various kinds of decay channels of heavy neutrino are evaluated when its mass is lighter than the mass of left handed gauge boson W_L. It is found that the total decay rate of heavy neutrino can be classified into left part dominance, right part dominance, and coexistence of left and right part. The results shows that when the heavy-light neutrino mixings is equaled to 1 and the mass of right handed gauge boson W_R is taken to be the lightest one satisfied by experiments, the total decay rate of heavy neutrino is still far smaller than its mass.

Key words: heavy neutrino, lepton number violation, decay rate, left-right symmetric model