Sterile neutrino dark matter in left-right theories

Abstract

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

Keywords

• Beyond Standard Model
• Cosmology of Theories beyond the SM
• Neutrino Physics