Top-quark FCNC decayt→cggin topcolor-assisted technicolor model

Abstract

The topcolor-assisted technicolor (TC2) model predicts several pseudoscalars called top-pions and at loop level they can induce the flavor-changing neutral-current (FCNC) top-quark decay t --> cgg which is extremely suppressed in the standard model (SM). We find that in the allowed parameter space the TC2 model can greatly enhance such a FCNC decay and push the branching ratio up to 10(-3), which is much larger than the predictions in the SM (10(-9)) and in the minimal supersymmetric model (10(-4)). We also compare the result with the two-body FCNC decay t --> cg and find that the branching ratio of t --> cgg is at the same order as t --> cg. Such enhanced FCNC top-quark decays may serve as a good probe of the TC2 model at the future top-quark factory.