Top-pions and single top production at HERA and THERA

We study single top quark production at the HERA and THERA colliders as coming from the FCNC vertices tcgamma and tcZ that appear at one loop level in Topcolor-assisted technicolor models (TC2). In contrast with previous expectations, we find that the production cross section is of order 10^-6 pb for HERA and 10^-4 pb for THERA (even lower that the SM prediction). Therefore, none of the two colliders are capable to probe the pseudoscalar top-pion or the scalar top-higgs predicted in TC2 models via single top production.