Top quark decay t→cbb-bar in topcolor-assisted technicolor models

The topcolor-assisted technicolor (TC2) model predicts the existence of the top-pions and the CP-even top-Higgs with large flavor-changing couplings to the top quark, which at tree-level can mediate the top quark three-body decay t→cbb-bar. We study this decay, show the dependence of the decay rate on the relevant TC2 parameters and compare the results with the predictions in the minimal supersymmetric model. We find that the decay rate in the TC2 model is much larger than that in the minimal supersymmetric model if the new particles are not too heavy. However, in consideration of the CDF and the LEP experiment limits, the top-pion mass is greater than 340 GeV in a more realistic parameter space, so the decay width of the channel t→cbb-bar intermediated by top-pions will be depressed greatly and difficult to be detected at the future collider. Thus, to observe this channel at the future collider, considering the top-Higgs contribution may be the possible way when the masses of the top-pions and the top-Higgs are not degenerate. (authors)