Single top production at HERA and THERA

We study the single top production mediated by flavor-changing neutral current via both of the t-q--γ and t-q-Z vertices (here q represents c and u quarks) in ep collisions at two colliders HERA and THERA. The contribution of the second vertex becomes even more important as the couplings take more improved values provided by the higher luminosities of colliders. In addition to these improvements, if the CM energy of the collider is also increased, the production will be dominated b y the anomalous t-q-Z vertex. (authors)