Bertuzzo, Enrico, Di Bari, Pasquale and Marzola, Luca
The problem of the initial conditions in flavoured
leptogenesis and the tauon N2-dominated scenario
Nuclear Physics B (doi:10.1016/j.nuclphysb.2011.03.027).
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We discuss the conditions to realise a scenario of ‘strong thermal leptogenesis,’ where the final asymmetry
is fully independent of the initial conditions, taking into account both heavy and light neutrino flavour
effects. In particular, the contribution to the final asymmetry from an initial pre-existing asymmetry has to
be negligible.We show that in the case of a hierarchical right-handed (RH) neutrino mass spectrum, the only
possible way is an N2-dominated leptogenesis scenario with a lightest RH neutrino mass M1 ?109 GeV
and with a next-to-lightest RH neutrino mass 1012 GeV?M2 ?109 GeV. This scenario necessarily requires
the presence of a heaviest third RH neutrino specie. Moreover, we show that the final asymmetry has
to be dominantly produced in the tauon flavour while the electron and the muon asymmetries have to be
efficiently washed-out by the lightest RH neutrino inverse processes. Intriguingly, such seemingly special
conditions for successful strong thermal leptogenesis are naturally fulfilled within SO(10)-inspired models.
Besides the tauon N2-dominated scenario, successful strong thermal leptogenesis is also achieved in scenarios
with quasi-degenerate RH neutrino masses. We also comment on the supersymmetric case. We also
derive an expression for the final asymmetry produced from leptogenesis taking fully into account heavy
neutrino flavour effects in the specific case M1 ?1012 GeV (heavy flavoured scenario), a result that can be
extended to any other mass pattern.
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