Successful leptogenesis inSO(10)unification with a left–right symmetric seesaw mechanism

Abstract

We study thermal leptogenesis in a broad class of supersymmetric SO(10) models with a leftright symmetric seesaw mechanism, taking into account flavour effects and the contribution of the next-to-lightest right-handed neutrino supermultiplet. Assuming M D = M u and a normal hierarchy of light neutrino masses, we show that four out of the eight right-handed neutrino mass spectra reconstructed from low-energy neutrino data can lead to successful leptogenesis with a reheating temperature in the (10 9 − 10 10 ) GeV range. In the remaining four solutions, leptogenesis is dominated by N 2 decays, as in the type I seesaw case. We find that some of these spectra can generate the observed baryon asymmetry for reheating temperatures above 10 10 GeV, in contrast to the type I case. Together with flavour effects, an accurate description of charged fermion masses turns out to be a crucial ingredient in the analysis.

Successful type I leptogenesis with -inspired mass relations

“…The comparison between our results and those in Ref. [10] is made difficult by the fact that there the type I see-saw case has been marginally studied as a limit of a more general left-right framework. We believe we have found regions of the parameter space where leptogenesis is successful, not fully investigated in Ref.…”

“…When this paper was being prepared, Ref. [10] appeared where flavored leptogenesis based on a mixed type I plus type II see-saw mechanism was studied. The comparison between our results and those in Ref.…”

“…Indeed, in a traditional version of leptogenesis, where the spectrum of righthanded (RH) neutrinos is hierarchical and the asymmetry is produced from the decays of the lightest ones, there is a stringent lower bound on their mass [6], M 1 > O(10 9 ) GeV, for a sufficiently large baryon asymmetry to be produced. On the other hand, SO (10) grand-unified theories typically yield, in their simplest version and for the measured values of the neutrino mixing parameters, a hierarchical spectrum with the RH neutrino masses proportional to the squared of the up-quark masses, leading to M 1 = O(10 5 ) GeV and to a final asymmetry that falls a few orders of magnitude below the observed one.…”

“…[7] for a detailed analysis. Furthermore, non-minimal versions of leptogenesis based on a mixed type I plus type II see-saw mechanism can be adopted [8,9,10]. It is nevertheless fair to say that a traditional type I picture of leptogenesis, where the spectrum is hierarchical and the asymmetry is generated from the decays of the lightest RH neutrinos, encounters serious difficulties within grand-unified SO(10) theories.…”

“…In Ref. [14] there were no specific quantitative and full calculations performed within SO (10). It was only shown that in general the wash-out from the lightest RH neutrinos may be small in some flavor even though the total washout is strong, while the CP asymmetry generated by the decays of the next-to-lightest RH neutrino was assumed to be maximal.…”