Effects of Top-Quark Anomalous Decay Couplings at \gamma \gamma   Colliders
  Most general tbW couplings were investigated in the process \gamma \gamma -> ttbar -> l^{+-} X for unpolarized photon beams. The double angular and energy distribution of the lepton was calculated and an optimal-observable analysis on it was carried out for the SM ttbar production mechanism. It was also shown that the leptonic angular distribution is insensitive to non-standard tbW vertex. That means that observation of non-standard effects indicates existence of some new physics in the production part. 
Kazumasa Ohkuma (Kobe Univ.)