Baryogenesis through Neutrino Oscillations: A Unified Perspective

Baryogenesis through neutrino oscillations is an elegant mechanism which has found several realizations in the literature corresponding to different parts of the model parameter space. Its appeal stems from its minimality and dependence only on physics below the weak scale. In this work we show that, by focusing on the physical time scales of leptogenesis instead of the model parameters, a more comprehensive picture emerges. The different regimes previously identified can be understood as different relative orderings of these time scales. This approach also shows that all regimes require a coincidence of time scales and this in turn translates to a certain tuning of the parameters, whether in mass terms or Yukawa couplings. Indeed, we show that the amount of tuning involved in the minimal model is never less than one part in 10^5. Finally, we explore an extended model where the tuning can be removed in exchange for the introduction of a new degree of freedom in the form of a leptophilic Higgs with a vacuum expectation value of the order of GeV.
Comment: 18 pages, 11 figures, submitted to Phys. Rev. D; corrected normalization in Fig. 11, coefficients in eq. 20-22 for consistency with definitions in Appendix B