Nuclear-structure corrections in superallowed $\beta$ decays

Compute the isospin-symmetry-breaking correction $\delta_{C}$ and the nuclear-structure-dependent radiative correction $\delta_{\mathrm{NS}}$ for the best-measured superallowed 0+ -> 0+ transitions (10C to 74Rb) with absolute uncertainty below $10^{-4}$, using ab initio methods with electroweak currents. Answer: corrected Ft values and $V_{ud}$, deciding whether the first-row CKM sum $\mid V_{ud}\mid^{2}+\mid V_{us}\mid^{2}+\mid V_{ub}\mid^{2}$ deviates from 1 (reported deficit of about 2 to 3 standard deviations).

Ab initio calculations of $\delta_C$ and $\delta_{\mathrm{NS}}$ for light emitters (10C, 14O) checked against measured isospin-breaking observables, then extended to heavier emitters.