Heavy right-handed neutrino dark matter in left-right models

We show that in a class of non-supersymmetric left-right extensions of the Standard Model (SM), the lightest right-handed neutrino (RHN) can 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 ×SU(2)L ×SU(2)R ×U(1)YL ×U(1)YR in which a heavy copy of the SM fermions is introduced and the stability of the RHN DM is guaranteed by an automatic Z2 symmetry present in the leptonic sector. In such models, the active neutrino masses are obtained via 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 a 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 Z2 symmetry and provides a concrete example of decaying DM interpretation of the PeV neutrinos observed at IceCube.