Modified Tri-bimaximal neutrino mixing confronted by JUNO $\theta_{12}$ measurement

TL;DR

This paper tests modified tri-bimaximal neutrino mixing patterns against new JUNO data, finding that one pattern aligns with observations and suggests an inverted neutrino mass hierarchy, with implications for future experiments.

Contribution

It introduces and evaluates minimal modifications to tri-bimaximal mixing in light of recent precise JUNO measurements, identifying a viable pattern consistent with current data.

Findings

Pattern c) fits data within 1σ

Pattern b) is disfavored at >3.5σ

Supports inverted neutrino mass hierarchy

Abstract

The JUNO collaboration has released its first measurement of reactor neutrino oscillations results, obtaining $\sin^2\theta_{12} = 0.3092\pm 0.0087$, an improvement in precision by a factor of 1.6 over previous combined results. We confront the minimally modified tri-bimaximal mixing pattern with the new data. Before the measurement of a non-zero $\theta_{13}$ mixing angle, the tri-bimximal mixing pattern is one of the most popular simple mixing scheme for neutrinos. Modifications have been proposed to keep some features of tri-bimaximal mixing and make it to be consistent with data. Minimal modifications preserving one column of the tri-bimaximal mixing matrix, yielding three patterns: a) unchanged third, b) unchanged second and c) unchanged first column. Pattern a) is excluded since it keeps $\theta_{13}=0$. Pattern b) predicts $V_{e2} = 1/\sqrt{3}$ and specific CP phase correlations, but JUNO's smaller $|V_{e2}|$ disfavors it at more than 3.5$\sigma$. Pattern c), predicting $V_{e2} = \cos\tau/\sqrt{3}$, can be in agreement with current data within 1$\sigma$, and implies $\sin^2\theta_{12} = (1-3\sin^2\theta_{13})/3(1-\sin^2\theta_{13})$ and CP violating quantity $\sin \theta = \pm 0.998$. The negative sign favors the inverted neutrino mass hierarchy. Upcoming experiments can further test this scenario.