  We study the production of a single top quark in association with a heavy
extra $Z'$ at hadron colliders in new physics models with and without
flavor-changing neutral-current (FCNC) couplings. We use QCD soft-gluon
resummation and threshold expansions to calculate higher-order corrections for
the total cross section and transverse-momentum distributions for $t Z'$
production. The impact of the uncertainties due to the structure of the proton
and scale dependence is also analyzed.
