Flavor-Changing Processes in Electroweak Theory.

We calculate the transitions q(,i)(--->)q(,j)+(gamma) and q(,i)(--->)q(,j) + gluon in one-loop approximation for the quarks with the flavors i (NOT=) j and arbitrary intermediate quark masses. The calculation is performed in a non-linear R(,(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 + (gamma) and s (--->) d + gluon, and some leptonic processes are given. We also present a new non-linear R(,(xi)) gauge which simplifies calculations involving Z boson. As an illustration the process s (--->) d + Z is treated in this gauge.