Right-handed neutrino dark matter in left-right symmetric models

We show that in a class of non-supersymmetric left-right extensions of the Standard Model (SM), the lightest right-handed neutrino (RHN) is naturally stable and can therefore play the role of thermal Dark Matter (DM) in the Universe for a wide mass range from TeV to PeV. Our model is based on the gauge group SU (3)(c) x SU(2)(L) x SU(2)(R) x U(1)(L), x U(1)(R), in which a heavy copy of the SM fermions are introduced and the stability of the RHN DM is guaranteed by an automatic Z(2) symmetry present in the leptonic sector. The active neutrino masses in the model arise from the type-II seesaw mechanism. We find a lower bound on the RHN DM mass of order TeV from relic density constraints, as well as an unitarity upper bound in the multi-TeV to PeV scale, depending on the entropy dilution factor. The RHN DM could be made long-lived by soft-breaking of the Z(2) symmetry and provides a concrete example of decaying DM interpretation of the PeV neutrinos observed at IceCube.