Three-jet distributions from the one-loop Zgg vertex at e⁺e^- colliders

The quark triangle loop can induce effective axial-vector Zgg coupling due to the large mass splitting between the top and the bottom quarks. We study its consequences in the three-jet decays of the Z-boson. Interference of the one-loop and the three-level Z → qqg amplitudes gives rise to deviations in various three-jet distributions, whose sign is opposite between the ccg and the bbg events. The largest difference between the charm and the bottom events is found to be at the level of 1%. The effect of the triangle loop near and above the top-quark threshold is briefly discussed.