  In this presentation we clarify some aspects of the LSZ formalism and wave
function renormalization for unstable particles in the presence of electroweak
interactions when mixing and CP violation are considered. We also analyze the
renormalization of the CKM mixing matrix which is closely related to wave
function renormalization. The effects due to the electroweak radiative
corrections that are described in this work are small, but they will need to be
considered when the precision in the measurement of the charged current sector
couplings reaches the 1% level. The work presented here is done in
collaboration with Julian Manzano and Pere Talavera.
