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

Abstract

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 ${\sin }^2{\theta }_{12}$ by JUNO already constrains part of these predictions, the remaining viable scenarios are primarily characterized by non-trivial correlations between ${\sin }^2{\theta }_{23}$ and the Dirac CP phase ${\delta }_{\mathrm{CP}}$, 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 ${\sin }^2{\theta }_{23}$--${\delta }_{\mathrm{CP}}$ 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 ${\sin }^2{\theta }_{23}$--${\delta }_{\mathrm{CP}}$ plane. We also evaluate, as a function of experimental exposure (determined by the run time), the fraction of ${\delta }_{\mathrm{CP}}$ values for which these theoretical predictions can be ruled out at more than $3\sigma$ CL. Our results show that the combined sensitivity of DUNE and Hyper-K provides a robust test of fixed-column lepton-mixing predictions.

30 pages, 11 figures