Physical renormalization condition for the quark-mixing matrix

We investigate the renormalization of the quark-mixing matrix in the electroweak standard model. The corresponding counterterms are gauge independent as can be shown using an extended BRS symmetry. Using rigid SU(2)(L) symmetry, we prove that the ultraviolet-divergent parts of the invariant counterterms are related to the field renormalization constants of the quark fields. We point out that for a general class of renormalization schemes rigid SU(2)(L) symmetry cannot be preserved in its classical form, but is renormalized by finite counterterms. Finally, we discuss a genuine physical renormalization condition for the quark-mixing matrix that is gauge independent and does not destroy the symmetry between quark generations.