Common Origin of Soft mu-tau and CP Breaking in Neutrino Seesaw and the Origin of Matter

TL;DR

This paper proposes that mu-tau and CP symmetries are fundamental and softly broken in the neutrino seesaw model, linking low-energy neutrino mixing angles and CP violation to cosmological matter-antimatter asymmetry.

Contribution

It introduces a unified soft-breaking origin for mu-tau and CP symmetries in the seesaw framework, predicting correlations between neutrino mixing angles and CP violation.

Findings

Predicted bounds on b8_{13}: 1^\u00b0 to 6^\u00b0

Established link between low-energy CP violation and leptogenesis

Revealed a hidden symmetry dictating solar mixing angle b8_{12}

Abstract

Neutrino oscillation data strongly support mu-tau symmetry as a good approximate flavor symmetry of the neutrino sector, which has to appear in any viable theory for neutrino mass-generation. The mu-tau breaking is not only small, but also the source of Dirac CP-violation. We conjecture that both discrete mu-tau and CP symmetries are fundamental symmetries of the seesaw Lagrangian (respected by interaction terms), and they are only softly broken, arising from a common origin via a unique dimension-3 Majorana mass-term of the heavy right-handed neutrinos. From this conceptually attractive and simple construction, we can predict the soft mu-tau breaking at low energies, leading to quantitative correlations between the apparently two small deviations \theta_{23} - 45^o and \theta_{13} - 0^o. This nontrivially connects the on-going measurements of mixing angle \theta_{23} with the upcoming experimental probes of \theta_{13}. We find that any deviation of \theta_{23} - 45^o must put a lower limit on \theta_{13}. Furthermore, we deduce the low energy Dirac and Majorana CP violations from a common soft-breaking phase associated with mu-tau breaking in the neutrino seesaw. Finally, from the soft CP breaking in neutrino seesaw we derive the cosmological CP violation for the baryon asymmetry via leptogenesis. We fully reconstruct the leptogenesis CP-asymmetry from the low energy Dirac CP phase and establish a direct link between the cosmological CP-violation and the low energy Jarlskog invariant. We predict new lower and upper bounds on the \theta_{13} mixing angle, 1^o < \theta_{13} < 6^o. In addition, we reveal a new hidden symmetry that dictates the solar mixing angle \theta_12 by its group-parameter, and includes the conventional tri-bimaximal mixing as a special case, allowing deviations from it.