Near-resonant thermal leptogenesis

A bstract We study leptogenesis in the quasi-degenerate but non-resonant regime. Expanding the CP asymmetry parameter near degeneracy and imposing the conservative non-resonance condition that the mass splitting must be much greater than the right-handed neutrino decay rates ∆ M > 100Γ i , yields the universal upper bound ϵ ≤ 1 / 200, independent of both the effective neutrino masses and the right-handed neutrino mass. We investigate vanilla and flavoured near-resonant leptogenesis and find that successful leptogenesis by right-handed neutrino decays can occur for M ≳ 100 GeV independent of washout regime, extending the viable parameter space of thermal leptogenesis down to the electroweak scale without invoking resonance. We also analyse near-resonant thermal leptogenesis during reheating and show that successful baryon asymmetry generation is compatible with reheating temperatures as low as T RH ≃ 10GeV without relying on non-thermal production. Finally, we present a consistent framework for incorporating flavour effects in near-resonant leptogenesis during reheating. Overall, near-resonant thermal leptogenesis offers a controlled alternative regime to resonant leptogenesis, lowering the leptogenesis scale to the electroweak scale, without reliance on a disputed regulator used in resonant leptogenesis.