  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
neutrinoless double beta decays, are mainly induced by the dimension-7 LNV
effective operator O_7=\bar l_R^c \gamma^\mu L_L(D_mu \Phi) \Phi \Phi. Note
that it is necessary to impose an Z_2 symmetry in order that O_7 dominates over
the conventional dimension-5 Weinberg operator, which naturally results in a
stable Z_2-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.
