Seesaw portal to super heavy dark matter with Z ₃ symmetry

Right-handed neutrinos N are introduced to explain the origin of the tiny neutrino masses via the seesaw mechanism. Required by relatively large Yukawa coupling and leptogenesis, masses of right-handed neutrinos are beyond 10 9 GeV. Such heavy right-handed neutrino can mediate the production of super heavy dark matter χ via the freeze-in mechanism. In the minimal Z 2 symmetric model, the right-hand neutrino portal interaction is y N ϕχ̅N with the dark scalar ϕ . One drawback of the Z 2 symmetric model is that the mass ordering m N > m ϕ with long-lived ϕ is almost ruled out by Big Bang Nucleosynthesis. In this paper, we propose that by extending the dark symmetry to Z 3 , one additional interaction y χ ϕχ̅ c χ is further allowed. In this way, the new decay mode ϕ → χχ would lead to the dark scalar ϕ being short-lived even with a feeble y χ , thus it is allowed by the cosmological constraints. The phenomenology of the Z 3 symmetric super heavy dark matter model is also studied in this paper.