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 $SU(3)_c \times SU(2)_L\times
SU(2)_R\times U(1)_{Y_L}\times U(1)_{Y_R}$ 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. 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 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.
