Connecting neutrino masses and dark matter by high-dimensional lepton number violation operator

Abstract

We propose a new model with the Majorana neutrino masses generated at two-loop level, in which the lepton number violation (LNV) processes, such as neutrino-less double beta decays, are mainly induced by the dimension-7 LNV effective operator $$ {\mathcal{O}}_7={\overline{l}}_R^c{\gamma}^{\mu }{L}_L\left({D}_{\mu}\varPhi \right)\varPhi \varPhi $$ . Note that it is necessary to impose an Z2 symmetry in order that $$ {\mathcal{O}}_7 $$ dominates over the conventional dimension-5 Weinberg operator, which naturally results in a stable Z2-odd neutral particle to be the cold dark matter candidate. More interestingly, due to the non-trivial dependence of the charged lepton masses, the model predicts the neutrino mass matrix to be in the form of the normal hierarchy. We also focus on a specific parameter region of great phenomenological interests, such as electroweak precision tests, dark matter direct searches along with its relic abundance, and lepton flavor violation processes.