SO(10)-inspired solution to the problem of the initial conditions in leptogenesis

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 Ô(0.1) requires: (i) reactor mixing angle 2° ≲ θ₁₃ ≲ 20°, in agreement with the experimental result θ = 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(J_CP) = -sign(η_B); (iv) neutrino masses m_i normally ordered; (v) lightest neutrino mass in the range m₁ ≈ 15–25 meV, corresponding to Σ_im_i ≈ 85–105 meV; (vi) neutrinoless double beta decay (0νββ) effective neutrino mass m_ee ≈ 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 m_ee ≈ 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.

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