On radiative corrections to lepton number violating processes

We consider the minimal model of the seesaw mechanism by introducing two right-handed neutrinos, whose masses are comparable to the electroweak scale. This framework is attractive, since it is testable at terrestrial experiments. A critical consequence of this mechanism is the violation of lepton number conservation due to the Majorana masses of both active neutrinos and heavy neutral leptons. In particular, we investigate the impact of the radiative corrections to Majorana masses of left-handed neutrinos on the lepton number violating processes, such as the neutrinoless double beta decay: $(Z, A) \to (Z+2,A) + 2 e^-$ and the inverse neutrinoless double beta decay: $e^- e^- \to W^- W^-$. It is shown that the cross section of the inverse neutrinoless double beta decay can increase by ${\cal O}(10)$~% when the masses of heavy neutral leptons are ${\cal O}(1)$~TeV, which has significant implications on future experiments.