Impact of flavour coupling on SO(10)-inspired leptogenesis

Abstract

We discuss the impact of flavour coupling on the predictions of low energy neutrino parameters from SO(10)-inspired leptogenesis (SO10INLEP). The righthanded (RH) neutrino mass spectrum is strongly hierarchical and successful leptogenesis relies on generating the asymmetry from next-to-lightest RH neutrino decays (N2-leptogenesis) and circumventing the lightest RH neutrino washout. These two conditions yield distinctive predictions such as a lower bound on the lightest neutrino mass m1 ≳ 1 meV. We first review the status of SO10INLEP, noticing how cosmological observations are now testing a particular neutrino mass window,m1 ≃ (10–30) meV, where only the first octant is allowed and a large range of values for the Dirac phase is excluded. Including flavour coupling, we find that the lower bound relaxes to m1 ≳ 0.65 meV. Moreover, new muon-dominated solutions appear slightly relaxing the upper bound on the atmospheric mixing angle. We also study the impact on strong thermal SO10INLEP (ST-SO10INLEP) scenario where, in addition to successful leptogenesis, one can washout a large pre-existing asymmetry. Contrarily to naive expectations, for which flavour coupling could jeopardise the scenario, allowing a large pre-existing asymmetry to survive unconditionally, we show, and explain analytically, that ST-SO10INLEP is still viable within almost the same allowed region of parameters. There is even a slight relaxation of the m1 viable window from (9–30)meV to (4–40)meV for a 10−3 pre-existing asymmetry. The new results from atmospheric neutrinos, mildly favouring normal ordering and first octant, are now in nice agreement with the predictions of ST-SO10INLEP. Intriguingly, the predicted 0νββ signal is starting to be within the reach of KamLAND-Zen.

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