Fate of θ 12 under μ − τ reflection symmetry in light of the first JUNO results

The recent Jiangmen Underground Neutrino Observatory (JUNO) measurements of θ 12 and Δ m 21 2 open a new avenue for probing flavor symmetric structures in the lepton sector. Motivated by this, we study a model in which μ − τ reflection symmetry naturally emerges from an underlying A 4 flavor symmetry within a type-II seesaw framework. Beyond its standard predictions of θ 23 = 4 5 ° and δ CP = ± π / 2 , the framework yields testable predictions for θ 12 that can be probed by JUNO. Two viable scenarios arise, one predicting sin 2 θ 12 ≳ 0.335 , which is strongly disfavored by the latest JUNO results. Correlations between θ 12 and model parameters further enhance the model’s predictivity. Future measurements at DUNE and T2HK will provide complementary tests of this scenario.