4/1/2023 0 Comments Vega conflict antimatter![]() ![]() In addition, the present neutrino data on δ and θ 23 can be explained better by the mixing symmetry. In particular, we show that the stringent condition of simultaneous maximality could be relaxed even with a very small departure from the exact μτ interchange. We show how these well known correlations will be changed if we generalize the μτ in- terchange symmetry to a μτ mixing symmetry. Both of them predict simultaneous maximality of δ and the atmospheric mixing angle θ 23. Within the framework of residual symmetry, two ℤ 2 type associate μτ inter- change symmetries robustly constrain the Dirac CP phase δ in a model independent way. 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. 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. We deduce conditions under which the baryon asymmetry produced by the second RH neutrino plays an important role. 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. The consideration of flavour effects due to the heavy neutrinos also translate into an upper bound on M1. This reduces the lower bound on the allowed values of M1, compared to what is stated in the literature. 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. We present a systematic study of leptogenesis in neutrino mass models with μτ-flavoured CP symmetry. We then briefly discuss how, in general, the mechanism leaves its imprints on the low energy CP phases and absolute light neutrino mass scale. We show that when effects of flavour on the washout processes are taken into account, the mechanism opens up the possibility of successful leptogenesis (gravitational) for a mass spectrum M 2 » 10 ⁹ GeV » M 1 with M 1 ≳ 6. In a minimal seesaw set up with two RH neutrinos, these washout processes are strong enough to erase a pre-existing asymmetry of significant magnitude. Primary threat to this gravity-induced lepton asymmetry to be able to successfully reproduce the observed baryon-to-photon ratio is the lepton number violating washout processes at T i ∼ M i. It is then natural to consider the viability of gravitational leptogenesis for a given RH mass spectrum which is not consistent with successful leptogenesis from decays. The frozen out asymmetry can act as a pre-existing asymmetry prior to the standard Fukugita-Yanagida leptogenesis phase ( T i ∼ M i, where M i is the mass of i th RH neutrino). However, when the temperature drops down, the interactions become weaker, and the asymmetry freezes out. At high temperature, lepton number violating scattering processes try to maintain a dynamically generated lepton asymmetry in equilibrium. Within the Type-I seesaw mechanism, quantum effects of the right-handed (RH) neutrinos in the gravitational background lead to an asymmetric propagation of lepton and anti-leptons which induces a Ricci scalar and neutrino Dirac-Yukawa coupling dependent chemical potential and therefore a lepton asymmetry in equilibrium. After a detail quantitative study of flavour effects, we show that the spectrum b) with a normal light neutrino mass ordering (which is now favoured by neutrino oscillation data) facilitates successful gravitational leptogenesis and the lightest RH mass scale can be lowered to ∼ 6.3 × 10 6 GeV. However, as mentioned earlier, N G0 B−L which is produced gravitationally survives the washout effects owing to the fast charged lepton interactions which reduce the strength of the dilution JHEP12(2020)067 factor D. For these spectrum of masses, it is well known that lepton asymmetry produced by RH neutrino decays is not adequate enough to be consistent with the observed baryon asymmetry, see e.g. Specifically, we consider two different hierarchical spectrum of RH masses, a) 10 9 GeV M 2 10 12 GeV T 0, M 1 10 9 GeV, i.e., M 2 is in the two flavour regime and M 1 is in the three flavour regime (we shall explain flavour regimes in detail in section 3) b) 10 12 GeV T 0 M 2, M 1 10 9 GeV, i.e., M 2 is in the unflavoured (one flavour) regime and M 1 is in the three flavour regime. ![]()
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