  Recently we have presented an analysis of flavor changing neutral coupling
mediated radiative top quark decays at next-to-leading order in QCD. In the
present paper we provide the details of the calculation of QCD corrections to
t-> q gamma and t-> q Z decays within the effective theory approach including
operator mixing. In particular, we calculate virtual matrix element corrections
and the corresponding bremsstrahlung contributions. In the case of t-> q gamma
we study the effects of kinematic cuts on the extracted branching ratios.
Analytical formulae are given at all stages of the calculation. We find that
the t-> q gamma decay can be used to probe also the effective operators
mediating t-> q g processes, since these can naturally contribute 10% or more
to the radiative decay, given typical experimental cuts on the decay kinematics
at hadron colliders. Conversely, we argue that any positive experimental signal
of the t-> q g process would indicate a natural lower bound on t-> q gamma
decay rate.
