Renormalization of the Cabibbo-Kobayashi-Maskawa Matrix
  Using the on-shell scheme and the general linear R_xi gauge we have calculated the one-loop amplitude W+ -> u_I d_j. In agreement with previous work we have shown that the Cabibbo-Kobayashi-Maskawa (CKM) matrix ought to be renormalized. We show how to renormalize the CKM matrix and, at the same time, obtain a gauge independent W decay amplitude. 
A. Barroso, L. Brucher, R. Santos