Flavoured leptogenesis and CPμτ symmetry

We present a systematic study of leptogenesis in neutrino mass models with μτ-flavoured CP symmetry. In addition to the strong hierarchical N1-dominated scenario (N₁DS) in the `two flavour regime' of leptogenesis, we show that one may choose the right-handed (RH) neutrino mass hierarchy as mild as M₂ ≃ 4.7M₁ for a perfectly valid hierarchical N₁DS. This reduces the lower bound on the allowed values of M₁, compared to what is stated in the literature. The consideration of flavour effects due to the heavy neutrinos also translate into an upper bound on M₁. It is only below this bound that the observed baryon-to-photon ratio can be realized for a standard N₁ domination, else a substantial part of the parameter space is also compatible with N₂DS. We deduce conditions under which the baryon asymmetry produced by the second RH neutrino plays an important role. Finally, we discuss another scenario where lepton asymmetry generated by N₂ in the two flavour regime faces washout by N₁ in the three flavour regime. Considering a hierarchical light neutrino mass spectrum, which is now favoured by cosmological observations, we show that at the end of N₁-leptogenesis, the asymmetry generated by N₂ survives only in the electron flavour and about 33% of the parameter space is consistent with a pure N₂-leptogenesis.