New calculations of neutron and kaon decays

Abstract

We describe two recent developments of the radiative correction theory in semileptonic beta decays. For neutron, a novel dispersive analysis of the γW -box diagram making use of neutrino scattering data leads to an improved precision and a shifted central value of V ud ; for kaon, an appropriate combination of meson form factors, lattice QCD inputs and chiral perturbation theory gives a much-improved determination of the radiative corrections in semileptonic kaon decays. These new calculations help to unveil/sharpen a series of anomalies in the measurements of V ud and Vus that may point towards the existence of new physics.