Effective field theory calculation of the QCD corrections to weak parameters

摘要

In the standard model the parameters (rho) and M(sub W)(sup 2)/M(sub Z)(sup 2)cos(sup 2)(theta) are unity at tree level. They are protected against large corrections by the so-called custodial symmetry. We investigate the symmetry breaking effect of effect of mass splittings in fermion doublets. The effective field theory method is applied to sum up the leading-log QCD corrections. We resolve a controversy concerning the scale at which the strong coupling constant is to be evaluated in the two-loop correction to electorweak parameters.