Abstract
We show that, within SO(10)-inspired leptogenesis, there exists a solution, with definite constraints on neutrino parameters, able simultaneously to reproduce the observed baryon asymmetry and to satisfy the conditions for the independence of the final asymmetry of the initial conditions (strong thermal leptogenesis). We find that the wash-out of a pre-existing asymmetry as large as O(0.1) requires: (i) reactor mixing angle 2°≲θ13≲20°, in agreement with the experimental result θ13=8°–10°; (ii) atmospheric mixing angle 16°≲θ23≲41°, compatible only with current lowest experimentally allowed values; (iii) Dirac phase in the range −π/2≲δ≲π/5, with the bulk of the solutions around δ≃−π/5 and such that sign(JCP)=−sign(ηB); (iv) neutrino masses mi normally ordered; (v) lightest neutrino mass in the range m1≃15–25 meV, corresponding to ∑imi≃85–105 meV; (vi) neutrinoless double beta decay (0νββ) effective neutrino mass mee≃0.8m1. All together this set of predictive constraints characterises the solution quite distinctively, representing a difficultly forgeable, fully testable, signature. In particular, the predictions mee≃0.8m1≃15 meV can be tested by cosmological observations and (ultimately) by 0νββ experiments. We also discuss different interesting aspects of the solution such as theoretical uncertainties, stability under variation of the involved parameters, forms of the orthogonal and RH neutrino mixing matrices.
Highlights
Leptogenesis [1,2] is a cosmological application of the see-saw mechanism [3], successfully linking two seemingly independent experimental observations: the matter–antimatter asymmetry of the Universe and the neutrino parameters tested in low energyP
In this paper we investigate in detail this potential feature of SO(10)-inspired models to realise successful strong thermal leptogenesis and we show that there exists a subset of the solutions leading to successful SO(10)-inspired leptogenesis that satisfies the strong thermal condition
When flavour effects are taken into account, and considering hierarchical RH neutrino mass patterns, as we are considering within SO(10)-inspired models, strong thermal leptogenesis can be realised only within a tauon-dominated N2-dominated scenario where the dominant contribution to the asymmetry is in the tauon flavour [12]
Summary
Leptogenesis [1,2] is a cosmological application of the see-saw mechanism [3], successfully linking two seemingly independent experimental observations: the matter–antimatter asymmetry of the Universe and the neutrino (masses and mixing) parameters tested in low energy. Flavour effects have an impact on the validity of the above mentioned neutrino mass window and in particular of the lower bound m1 10−3 eV, originating from an intriguing conspiracy between the measured atmospheric and solar neutrino mass scales and the condition of successful strong thermal leptogenesis. A solution to the requirement of successful strong thermal leptogenesis still exists, but the conditions for its realisation become seemingly quite special First of all they imply a tauon N2-dominated scenario, where the final asymmetry is produced by the next-to-lightest RH neutrinos in the two-flavour regime, implying 1012 GeV M2 109 GeV, dominantly in the tauon flavour and where the lightest RH neutrino mass M1 109 GeV. This scenario corresponds to a very well theoretically motivated set of (SO(10)-inspired) conditions that over-constrains the see-saw parameter space In this way the final asymmetry becomes much more sensitive to the low energy neutrino parameters than in the general case.
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