Exploring the Anomalous Higgs-top Couplings

TL;DR

This paper proposes a new observable in top pair Higgs production at the LHC to probe anomalous Higgs-top couplings, aiming to detect deviations from the Standard Model and constrain scalar and pseudoscalar components.

Contribution

It introduces an asymmetry-like observable $O_{\phi}$ to distinguish scalar and pseudoscalar Higgs-top couplings and links pseudoscalar components to measurable top quark EDM limits.

Findings

The observable $O_{\phi}$ can effectively differentiate scalar and pseudoscalar couplings.

Future electron-positron colliders could set strong limits on Higgs-top coupling parameters.

A top EDM limit of $10^{-19}$ e.cm can exclude significant regions of the coupling parameter space.

Abstract

Top quark with its large Yukawa coupling is crucially important to explore TeV scale physics. Therefore, the study of Higgs-top sector is highly motivated to look for any deviations from the standard model predictions. The most general lowest order Lagrangian for the Higgs-top Yukawa coupling has scalar ($\kappa$) and pseudoscalar ($\tilde{\kappa}$) components. Currently, these couplings are constrained indirectly using the present experimental limits on the Higgs-$\gamma$-$\gamma$ and Higgs-gluon-gluon couplings. Furthermore, stronger bounds on $\kappa$ and $\tilde{\kappa}$ are obtained using the limits on the electric dipole moments (EDM). In this work, we propose an asymmetry-like observable $O_{\phi}$ in $t\bar{t}H$ production at the LHC to probe the Higgs-top coupling and to distinguish between the scalar and pseudoscalar components. We also show that the presence of the pseudoscalar component in the Higgs-top Yukawa coupling leads to a sizeable value for the top quark EDM. It is shown that a limit of $10^{-19}$ e.cm, which is achievable by the future $e^{-}e^{+}$ collider, allows us to exclude a significant region in the $(\kappa,\tilde{\kappa})$ plane.