Testing residual-symmetry-fixed columns of $U_{\rm PMNS}$ at DUNE and T2HK with initial JUNO constraints

TL;DR

This paper investigates how upcoming neutrino experiments DUNE and T2HK can test specific predictions of lepton mixing matrices derived from residual symmetries, especially focusing on correlations between mixing angles and CP phase.

Contribution

It provides detailed simulations and analysis of how future experiments can validate or refute fixed-column lepton mixing predictions from residual symmetries, incorporating recent JUNO constraints.

Findings

Combined DUNE and T2HK data can robustly test fixed-column predictions.

Precise $ heta_{23}$-$ m \delta_{CP}$ correlations are key to testing models.

Experiment sensitivity varies with exposure and parameter correlations.

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 ones are primarily characterized by non-trivial correlations between $\sin^{2}\theta_{23}$ and the Dirac CP phase $\delta_{\rm CP}$, which are currently only weakly constrained. This motivates a detailed investigation using next-generation long-baseline neutrino experiments. For the viable scenarios, we derive precise $\sin^{2}\theta_{23}$-$\delta_{\rm CP}$ correlations and use them to generate test-event samples, marginalising over the remaining oscillation parameters. We perform detailed simulations for DUNE and T2HK, presenting allowed regions in the $\sin^{2}\theta_{23}$-$\delta_{\rm CP}$ plane and evaluating the CP-violation fraction as a function of exposure. Our results show that the combined sensitivity of DUNE and T2HK provides a robust test of fixed-column lepton-mixing predictions.