Leptonic first-row correlation and unitarity waiting for further JUNO tests

We conjecture that there exists a remarkable correlation among the three elements in the first row of the $3\times 3$ lepton flavor mixing matrix $U$: $\mathrm{\mid }{U}_{e1}^{}{\mathrm{\mid }}^2=2(\mathrm{\mid }{U}_{e2}^{}{\mathrm{\mid }}^2+\mathrm{\mid }{U}_{e3}^{}{\mathrm{\mid }}^2)$, which holds even though $U$ is non-unitary in the canonical seesaw mechanism. This ``first-row correlation" is fully consistent with ${\sin }^2{\theta }_{12}^{}=(1-2{\tan }^2{\theta }_{13}^{})\mathrm{/}3$ in the unitarity limit of $U$, as supported by the latest JUNO and Daya Bay precision measurements at a confidence level close to $1\sigma$.