Azimuthal angular dependence of decay lepton in e+ e- --> t tbar
  We discuss top quark production and its subsequent decay for searching new physics at lepton colliders. The angular dependence of the decay leptons is calculated including both QCD corrections and anomalous gamma Z - t tbar couplings. The off-diagonal spin basis for the top and anti-top quarks is shown to be useful to probe the anomalous couplings. 
Yuichiro Kiyo, Jiro Kodaira, Kazushige Morii