Top-quark Yukawa coupling with a dimension-6 operator

TL;DR

This paper introduces a dimension-6 operator to the top-quark Yukawa coupling, incorporating CP violation and new interactions, and studies their effects on collider processes and unitarity bounds.

Contribution

It extends the standard model by adding a CP-violating dimension-6 operator to the top Yukawa coupling, analyzing its phenomenological implications.

Findings

New $ttHH$ contact interaction identified

Unitarity bounds on the operator coefficient derived

Impact on muon collider process studied

Abstract

We 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 $\mu^-\mu^+\to \nu_\mu\bar{\nu}_\mu t\bar{t}H$ compared with the standard dimension-4 top-Yukawa coupling. The unitarity bounds on the coefficient of the new physics operator is obtained from $W^-_LW^+_L$ and $HH$ initiated processes.