A diagnostic strategy for testing whether beyond-standard-model non-unitary neutrino mixing can reconcile the mild disagreement between the NOvA and T2K long-baseline oscillation experiments in the sin^2(theta23)-delta_CP plane. Instead of fitting all non-unitary parameters simultaneously (which obscures cause and effect), the analysis switches on a single parameter of the lower-triangular non-unitary factor at a time - alpha_00, alpha_10, or alpha_11, chosen because they most affect the electron-(anti)neutrino appearance probabilities - and asks whether it enlarges the overlap of the two experiments' allowed regions. The result isolates alpha_10 as the parameter that genuinely resolves the tension, with a best-fit |alpha_10| near 0.06 for the normal hierarchy accepted by both experiments at 1 sigma, whereas alpha_00 enlarges the overlap yet leaves NOvA ruling out unitary mixing at 3 sigma while T2K prefers it. The contribution is both the isolation methodology and its physical interpretation via the effect of each parameter on oscillation probabilities, together with projections for a combined NOvA+T2K fit and the upcoming DUNE experiment under the non-unitary assumption.
This physics letter uses a non-unitary three-flavor neutrino mixing scheme to address the mild tension between the NOvA and T2K long-baseline oscillation experiments, whose 1-sigma allowed regions in…