Remark on a Generic and Natural Model of Neutrinos
We comment on what the naturalness argument of ’t Hooft implies for a minimal extension of the standard model which incorporates right-handed neutrinos with generic mass terms. If this Lagrangian is taken as a low energy effective theory, the naturalness argument of ’t Hooft implies pseudo-Dirac neutrinos with very small masses. This argument is based on an observation that the right-handed components of neutrinos in the massless limit exhibit an enhanced symmetry which is reminiscent of the Nambu-Goldstone fermions associated with spontaneously broken supersymmetry. The conventional seesaw scenario gives another natural solution if the heavy right-handed neutrinos are integrated out in defining a low energy effective theory.