Unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix is one of the cornerstones of the Standard Model (SM), a rigorous mathematical expression of the universality of the weak interaction across quark and lepton sectors. Recent reanalysis of the SM radiative corrections to beta decays of the free neutron, nuclei and kaons led to an unexpected 3-5 sigma deficit in the unitarity constraint on the top-row elements of the CKM matrix. The recent developments in the theory of 1-loop SM radiative corrections concern hadronic and nuclear contributions. The new approach to nonperturbative QCD effects combines lattice QCD, Regge theory, effective field theory methods and modern nuclear theory computations with dispersion theory and allows for a robust error estimation. With these improvements, beta decays remain a sensitive tool for searches for physics beyond the Standard Model.
IFIC seminar organizers