Partial μ-τ Reflection Symmetry and Its Verification at DUNE and Hyper-Kamiokande

We study origin, consequences and testability of a hypothesis of `partial μ-τ' reflection symmetry. This symmetry predicts |Uμi|=|Uτi| (i=1,2,3) for a single column of the leptonic mixing matrix U. Depending on whether this symmetry holds for the first or second column of U different correlations between θ23 and δCP can be obtained. This symmetry can be obtained using discrete flavour symmetries. In particular, all the subgroups of SU(3) with 3-dimensional irreducible representation which are classified as class C or D can lead to partial μ-τ reflection symmetry. We show how the predictions of this symmetry compare with the allowed area in the $\sin^2\theta_{23} - \dcp$ plane as obtained from the global analysis of neutrino oscillation data. Furthermore, we study the possibility of testing these symmetries at the proposed DUNE and Hyper-Kamiokande (HK) experiments (T2HK, T2HKK), by incorporating the correlations between θ23 and δCP predicted by the symmetries. We find that when simulated data of DUNE and HK is fitted with the symmetry predictions, the $\theta_{23}-\dcp$ parameter space gets largely restricted near the CP conserving values of δCP. Finally, we illustrate the capability of these experiments to distinguish between the two cases leading to partial μ−τ symmetry namely |Uμ1|=|Uτ1| and |Uμ2|=|Uτ2|.