Effective neutrino mass operators: a guide to model building

Effective operators relevant for generating small Majorana masses for the neutrinos in the Standard Model will be considered. These operators serve as a useful guide for building models of neutrino mass. Some of these operators are represented by familiar models in the literature, and others lead to interesting new models. The number of the relevant operators will be drastically reduced if neutrinoless double beta decays are observed in current experiments.