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The problem of the initial conditions in flavoured leptogenesis and the tauon N2-dominated scenario

By Enrico Bertuzzo, Pasquale Di Bari and Luca Marzola


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

Topics: QA, QC
Year: 2011
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Provided by: e-Prints Soton
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