Flavor Changing Neutral Coupling Mediated Radiative Top Quark Decays at Next-to-Leading Order in QCD

We compute the branching ratios for the rare top quark decays t to c gamma and t to c Z mediated by effective flavor changing neutral couplings at the next-to-leading order in QCD including the effects due to operator mixing. After re-suming contributions of order [alpha_s log (Lambda / m_t)]^n, where Lambda is the scale at which the effective operators are generated, at leading log level using renormalization group methods, we compute finite matrix element corrections and study the effects of experimental kinematic cuts on the extracted branching ratios. We find that the t to c gamma decay can be used to probe also the effective operators mediating t to c g processes, since these can naturaly contribute 10% or more to the radiative decay. Conversely, any experimental signal of t to c g would indicate a natural lower bound on t to cZ, gamma.