Is first-row CKM unitarity violated (Cabibbo angle anomaly)?

Test $\left|V_{ud}\right|^2 + \left|V_{us}\right|^2 + \left|V_{ub}\right|^2 = 1$, with $V_{ud}$ from superallowed $0+$ to $0+$ nuclear beta decays and neutron decay, and $V_{us}$ from K_l3, K_mu2/pi_mu2 and $\tau$ decays. The current deficit is of order $10^{-3}$ at about $3\sigma$, together with an internal K_l3 versus K_mu2 tension; an answer is confirmation above $5\sigma$ or resolution to below $2\sigma$.

Improved electroweak radiative corrections and nuclear-structure corrections for superallowed decays, new lattice QCD form factors for K_l3, and new K_l3/K_mu2 ratio measurements (NA62).