Searches for flavor-changing neutral currents and single top quarks at D0

I present brief descriptions of two top quark analyses performed using D0 data from p{bar p} collisions at {radical}s = 1.96 TeV: the search for flavor-changing neutral-current couplings (FCNC) of the top quark with a charm or an up quark with the exchange of a gluon, and the search for the standard model production of single top quarks. The search for FCNC couplings of a gluon to the top quark is the first such analysis at hadron colliders. I describe the application of the Bayesian approach for comparing our physics models to the observed data in both analyses and, in one of them, to separate small signals from large backgrounds