Dirac phase leptogenesis

TL;DR

This paper explores leptogenesis driven solely by the Dirac CP phase in the PMNS matrix, analyzing how neutrino mass spectra influence the generation of the universe's matter-antimatter asymmetry.

Contribution

It provides a detailed analysis of Dirac phase leptogenesis, highlighting the effects of hierarchical and quasi-degenerate neutrino spectra on CP asymmetry and baryon asymmetry.

Findings

Hierarchical spectrum leads to small allowed regions and initial condition dependence.

Quasi-degenerate spectrum enhances CP asymmetry and removes initial condition dependence.

Resonant leptogenesis sets a lower bound on _{13} depending on the lightest neutrino mass.

Abstract

I present here a concise summary of the preprint arXiv:0707.3024, written in collaboration with A. Anisimov and P. Di Bari. There we discuss leptogenesis when {\em CP} violation stems exlusively from the Dirac phase in the PMNS mixing matrix. Under this assumption it turns out that the situation is very constrained when a hierarchical heavy right-handed (RH) neutrino spectrum is considered: the allowed regions are small and the final asymmetry depends on the initial conditions. On the other hand, for a quasi-degenerate spectrum of RH neutrinos, the {\em CP} asymmetry can be enhanced and the situation becomes much more favorable, with no dependence on the initial conditions. Interestingly, in the extreme case of resonant leptogenesis, in order to match the observed baryon asymmetry of the Universe, we obtain a lower bound on \sin \q_{13} which depends on the lightest active neutrino mass m_1.