Model-independent determination of nuclear weak form factors and implications for Vud and CKM unitarity

We analyze the recoil corrections in superallowed beta decays of $T=1$, $J^P=0^+$ nuclei by fixing the mean square charge weak radius model-independently using the data of multiple charge radii across the nuclear isotriplet. We argue that the existing theory uncertainty in the statistical rate function $f$ might have been substantially underestimated. We discuss its possible impact on precise Vud determination and first-row CKM unitarity.