Effective fermion-Higgs interactions at an $e^+e^-$ collider with polarized beams

TL;DR

This paper explores potential new physics interactions involving the Higgs boson and fermions at future electron-positron colliders, proposing observables to constrain these interactions and analyzing the impact of beam polarization on sensitivity.

Contribution

It provides the most general form of fermion-Higgs effective vertices, derives differential cross sections, and assesses how polarized beams improve the sensitivity to new physics couplings.

Findings

Derived limits on effective couplings at 500 GeV collider

Identified observables with CP and T properties for probing interactions

Showed polarization enhances sensitivity by a factor of 2-4

Abstract

We consider the possibility of new physics giving rise to effective interactions of the form $e^+e^-Hf \bar f$, where $f$ represents a charged lepton $\ell$ or a (light) quark $q$, and $H$ the recently discovered Higgs boson. Such vertices would give contributions beyond the standard model to the Higgs production processes $e^+e^- \to H\ell^+\ell^-$ and $e^+e^- \to H q \bar q$ at a future $e^+e^-$ collider. We write the most general form for these vertices allowed by Lorentz symmetry. Assuming that such interactions contribute in addition to the standard model production processes, where the final-state fermion pair comes from the decay of the $Z$ boson, we obtain the differential cross section for the processes $e^+e^- \to H\ell^+\ell^-$ and $e^+e^- \to Hq\bar q$ to linear order in the effective interactions. We propose several observables with differing CP and T properties which, if measured, can be used to constrain the couplings occurring in interaction vertices. We derive possible limits on these couplings that may be obtained at a collider with centre-of-mass energy of 500 GeV and an integrated luminosity of 500 fb$^{-1}$. We also carry out the analysis assuming that both the electron and positron beams can be longitudinally polarized, and find that the sensitivity to the couplings can be improved by a factor of 2-4 by a specific choice of the signs of the polarizations of both the electron and positron beams for the same integrated luminosity.