Top-quark Yukawa coupling with a dimension-6 operator

\nWe extend the standard top-quark Yukawa coupling with a dimension-6 operator in order to accommodate a CP violating complex phase with manifest gauge invariance. This leads to a new ttHH contact interaction, along with many Goldstone boson couplings. We investigate the impact of the new interactions on a muon collider process µ−µ+ → νµῡµtt¯H compared with the standard dimension-4 top-Yukawa coupling. The unitarity bounds on the coefficient of the new physics operator is obtained from WL−W+L and HH initiated processes.