Abstract

In realistic unified models involving so-called SO(10)-inspired patterns of Dirac and heavy right-handed (RH) neutrino masses, the lightest right-handed neutrino N1 is too light to yield successful thermal leptogenesis, barring highly fine tuned solutions, while the second heaviest right-handed neutrino N2 is typically in the correct mass range. We show that flavour coupling effects in the Boltzmann equations may be crucial to the success of such N2 dominated leptogenesis, by helping to ensure that the flavour asymmetries produced at the N2 scale survive N1 washout. To illustrate these effects we focus on N2 dominated leptogenesis in an existing model, the A to Z of flavour with Pati-Salam, where the neutrino Dirac mass matrix may be equal to an up-type quark mass matrix and has a particular constrained structure. The numerical results, supported by analytical insight, show that in order to achieve successful N2 leptogenesis, consistent with neutrino phenomenology, requires a ``flavour swap scenario'' together with a less hierarchical pattern of RH neutrino masses than naively expected, at the expense of some mild fine-tuning. In the considered A to Z model neutrino masses are predicted to be normal ordered, with an atmospheric neutrino mixing angle well into the second octant and the Dirac phase δ≃ 20̂, a set of predictions that will be tested in the next years in neutrino oscillation experiments. Flavour coupling effects may be relevant for other SO(10)-inspired unified models where N2 leptogenesis is necessary.

Highlights

  • It would be certainly desirable to extend the SM, realising a unified picture able to solve the flavour problem, explaining masses and mixing parameters of quarks and leptons, and at the same time to provide solution to the cosmological puzzles

  • The A to Z model can provide a satisfactory fit to all parameters in the leptonic mixing matrix but can reproduce the correct value of the matter-antimatter asymmetry with N2-dominated leptogenesis. In this respect it is crucial to account for flavour coupling effects due to the redistribution of the asymmetry in particles that do not participate directly to the generation of the asymmetry, in primis the Higgs asymmetry

  • In particular a “flavour swap” scenario is realised whereby the asymmetry generated in the tauon flavour emerges as a surviving asymmetry dominantly in the muon flavour

Read more

Summary

Introduction

It would be certainly desirable to extend the SM, realising a unified picture able to solve the flavour problem, explaining masses and mixing parameters of quarks and leptons, and at the same time to provide solution to the cosmological puzzles. The right-handed (RH) neutrino mass spectrum in this model is very hierarchical, typical of SO(10)-inspired models (assuming type I seesaw) In this way the lightest RH neutrino N1 is too light to generate a sizeable asymmetry [8] while on the other hand the next-to-lightest RH neutrino is heavy enough to be able potentially to generate the correct asymmetry realising the so called N2 dominated scenario [9, 10, 11, 12] or N2 leptogenesis.

Neutrino masses in the A to Z model
Fitting neutrino parameters
Leptogenesis without flavour coupling
Leptogenesis with flavour coupling
M1 matm 16 π v2
Conclusions
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call