Superheavy dark matter within the seesaw framework

Superheavy right-handed neutrinos are known to provide an economical solution to generate the mass of the light neutrinos as well as a lepton asymmetry through to their decay in the early Universe that gets subsequently converted into a baryon asymmetry. Another missing piece of the Standard Model is dark matter, which can also be superheavy provided that the particle lifetime is anomalously long, i.e. greater than 10²²~yr. Relying on two variants of the seesaw framework, and assuming slight mixing in the right-handed neutrino sector, we show that the resulting Majorana mass eigenstates with mass MX can be dark matter candidates provided that the mass mixing parameter δ M satisfies approximately δ M 2× 10⁻¹⁷/[MX/(10⁹~GeV)]0.5~GeV for MX 10⁹~GeV. Some implications in the context of inflationary cosmologies are discussed.