Quasidegeneracy of Majorana Neutrinos and the Origin of Large Leptonic Mixing

TL;DR

This paper suggests that the large leptonic mixing observed in neutrinos may originate from a near-degenerate Majorana neutrino mass spectrum, with small mass differences explaining the measured mixing angles and CP violation.

Contribution

It introduces a novel scenario where quasidegenerate Majorana neutrinos naturally produce large leptonic mixing and CP violation, linking mass degeneracy breaking to observable phenomena.

Findings

Lifting neutrino mass degeneracy explains the measured mixing angles.

The scenario predicts potentially detectable leptonic CP violation.

Correlations among observables support the model's viability.

Abstract

We propose that the observed large leptonic mixing may just reflect a quasidegeneracy of three Majorana neutrinos. The limit of exact degeneracy of Majorana neutrinos is not trivial, as leptonic mixing and even CP violation may occur. We conjecture that the smallness of $|U_{13}|$, when compared to the other elements of $U_{PMNS}$, may just reflect the fact that, in the limit of exact mass degeneracy, the leptonic mixing matrix necessarily has a vanishing element. We show that the lifting of the mass degeneracy can lead to the measured value of $|U_{13}|$ while at the same time accommodating the observed solar and atmospheric mixing angles. In the scenario we consider for the breaking of the mass degeneracy there is only one CP violating phase, already present in the limit of exact degeneracy, which upon the lifting of the degeneracy generates both Majorana and Dirac-type CP violation in the leptonic sector. We analyse some of the correlations among physical observables and point out that in most of the cases considered, the implied strength of leptonic Dirac-type CP violation is large enough to be detected in the next round of experiments.