Testing predictions of discrete flavour and modular symmetries at DUNE and Hyper-K with JUNO constraints

A

bstract

We study fixed-column predictions of the lepton mixing matrix that arise from residual symmetries originating in a class of discrete flavour and modular symmetries. While the recent high-precision determination of sin ² θ ₁₂ by JUNO already constrains part of these predictions, the remaining viable scenarios are primarily characterized by non-trivial correlations between sin ² θ ₂₃ and the Dirac CP phase δ _CP , which are currently only weakly constrained. This motivates a detailed investigation of the sensitivities of next-generation long-baseline neutrino experiments to these scenarios. For the phenomenologically viable fixed-column predictions that can constitute a column of the lepton mixing matrix, we derive precise sin ² θ ₂₃ - δ _CP correlations and use them to generate test-event samples, marginalising over the remaining oscillation parameters. We perform detailed simulations for DUNE and Hyper-K, presenting the allowed regions in the sin ² θ ₂₃ - δ _CP plane. We also evaluate, as a function of experimental exposure (determined by the run time), the fraction of δ _CP values for which these theoretical predictions can be ruled out at more than 3 σ CL. Our results show that the combined sensitivity of DUNE and Hyper-K provides a robust test of fixed-column lepton-mixing predictions.