The most precise value of the top-left corner element of the CKM matrix $V_{ud}$ is obtained from superallowed nuclear beta decays. Observed hints to a $2.5-3\sigma$ deficit in top-row CKM unitarity motivated a reanalysis of nuclear corrections. These latter use nuclear charge radii as input, and so do their uncertainties. An extraction of nuclear charge radii from atomic measurements entails...
For decades, muonic atom spectroscopy has provided absolute values of nuclear RMS radii. The recent restart of muonic atom measurements also led to refinements in theoretical predictions. In my presentation, I will show the latest results for heavy muonic atoms, comparing them with previous results and focusing on individual and overall uncertainties. Finally, I will discuss how recent...
