Sterile neutrino dark matter in left-right theories

Abstract

Abstract SU(2)L× SU(2)R gauge symmetry requires three right-handed neutrinos (Ni), one of which, N1, can be sufficiently stable to be dark matter. In the early universe, WR exchange with the Standard Model thermal bath keeps the right-handed neutrinos in thermal equilibrium at high temperatures. N1 can make up all of dark matter if they freeze-out while relativistic and are mildly diluted by subsequent decays of a long-lived and heavier right-handed neutrino, N2. We systematically study this parameter space, constraining the symmetry breaking scale of SU(2)R and the mass of N1 to a triangle in the (vR, M1) plane, with vR = (106− 3 × 1012) GeV and M1 = (2 keV–1 MeV). Much of this triangle can be probed by signals of warm dark matter, especially if leptogenesis from N2 decay yields the observed baryon asymmetry. The minimal value of vR is increased to 108 GeV for doublet breaking of SU(2)R, and further to 109 GeV if leptogenesis occurs via N2 decay, while the upper bound on M1 is reduced to 100 keV. In addition, there is a component of hot N1 dark matter resulting from the late decay of N2→ N1ℓ+ℓ− that can be probed by future cosmic microwave background observations. Interestingly, the range of vR allows both precision gauge coupling unification and the Higgs Parity understanding of the vanishing of the Standard Model Higgs quartic at scale vR. Finally, we study freeze-in production of N1 dark matter via the WR interaction, which allows a much wider range of (vR, M1).