Heavy Chiral Fermions and Dark Matter

Figure 1

Relative relic density 𝑟_Ω of stable fourth-generation neutrino 𝜒₁ as a function of its mass for mixing angle values 𝜃=10^∘ (solid), 20^∘ (dashed), 30^∘ (dotted), and 40^∘ (dot-dashed). The shaded region is excluded by LEP-2 data [1] in the case of 𝜒₁ being a Dirac fermion. Plot from [10].