Probe of the Wtb coupling in t(t)over-bar pair production at linear colliders

The Wtb vertex can be probed on future colliders in the processes of single top production (LHC, pp mode, NLC, gamma e mode) and of top pair productio n (NLC, e(+)e(-) mode). We analyze observables sensitive to anomalous Wtb c ouplings in the top pair production process of e(+)e(-) collisions. In part icular, forward-backward and spin-spin asymmetries of the top decay product s and the asymmetry of the lepton energy spectrum are considered. Possible bounds on anomalous couplings obtained are competitive to those expected fr om the upgraded Tevatron and LHC. The validity of the infinitely small widt h approximation for the three-body top decay is also studied in detail.