Top flavour-changing neutral coupling signals at a linear collider

We present an analysis of the sensitivity of the TESLA e+e- collider to top flavour-changing neutral couplings to the Z boson and photon. We consider the cases without beam polarization, with only e- polarization and with e- and e+ polarization, showing that the use of the latter substantially enhances the sensitivity to discover or bound these vertices. For some of the couplings the expected LHC limits could be improved up to an order of magnitude for equal running times. (orig.)