Probing New Physics with the Electron Yukawa coupling

TL;DR

This paper explores the potential to measure or constrain the electron Yukawa coupling at future colliders and intensity experiments, highlighting the challenges and possible new physics scenarios that could alter this coupling.

Contribution

It investigates how the electron Yukawa coupling can be enhanced in simplified UV models and compares the effectiveness of collider and intensity frontier experiments in probing these deviations.

Findings

$(g-2)_e$ can effectively probe the electron Yukawa in some models.

Certain models predict large deviations in the electron Yukawa coupling.

Dedicated Higgs pole runs are necessary for some scenarios.

Abstract

A dedicated run of a future electron-positron collider (FCC-ee) at a center-of-mass energy equal to the Higgs boson mass would enable a direct measurement of the electron Yukawa coupling. However, it poses substantial experimental difficulties due to large backgrounds, the requirement for monochromatised $e^+e^-$ beams, and the potential extension of the FCC-ee timeline. Given this, we explore the extent to which the electron Yukawa coupling can be enhanced in simplified UV models and examine whether such scenarios can be constrained by other FCC-ee runs or upcoming experiments at the intensity frontier. Our results indicate that in certain classes of models, the $(g-2)_e$ provides a probe of the electron Yukawa coupling that is as effective or better than the FCC-ee. Nevertheless, there exist models that can lead to sizeable deviations in the electron Yukawa coupling which can only be probed in a dedicated run at the Higgs pole mass.