Theoretical approaches relevant to neutrinoless double beta decay*

Search for neutrinoless double beta decay is one of the primary probes to understand the nature of neutrino mass. Its discovery implies lepton-number violation, confirming the Majorana neutrino mass which is realized by introducing sterile neutrinos. The theoretical approach requires somewhat complicated processes connecting fundamental interactions to those at hadronic and nuclear levels. In this talk, I will discuss the systematic analysis of the neutrinoless double beta decay process based on effective field theory including sterile neutrinos, and present its application to a realistic model.