Modified tri-bimaximal neutrino mixing confronted by JUNO θ12 measurement

The JUNO collaboration has released its first measurement of reactor neutrino oscillations, obtaining sin θ 12 2 = 0.3092 ± 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 nonzero θ 13 mixing angle, the tri-bimaximal mixing pattern was 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 θ 13 = 0 . Pattern b) predicts V e 2 = 1 / 3 and specific CP-phase correlations, but JUNO’s smaller | V e 2 | disfavors it at more than 3.5 σ . Pattern c), predicting V e 2 = cos τ / 3 , can be in agreement with current data within 1 σ . It implies sin 2 θ 12 = ( 1 − 3 sin 2 θ 13 ) / 3 ( 1 − sin 13 2 ) and CP violating quantity sin δ CP ∼ ± 1. The current central values of NuFIT 6.1 for neutrino mixing data indicate the model with sin δ C P ≈ − 1 fits data better which then requires neutrino mass to the inverted hierarchy. Upcoming experiments can further test this scenario and raise the confidence level to rule in or rule out the model.