Flavor-changing processes in electroweak theory

The transitions q/sub i/ → q/sub j/ + γ and q/sub i/ → q/sub j/ + gluon in one-loop approximation are calculated for the quarks with the flavors i not equal to j and arbitrary intermediate quark masses. The calculation is performed in a nonlinear R/sub xi/ gauge. The reduced number of Feynman diagrams as well as simplified Ward identities greatly facilitate the calculation. Some applications of our calculation to the processes s → d + γ and s → d + gluon, and some leptonic processes are given. A new non-linear R/sub xi/ gauge is presented which simplifies calculations involving Z boson. As an illustration the process s → d + Z is treated in this gauge