Interplay between new physics in one-loop Higgs couplings and the top-quark Yukawa coupling

TL;DR

This paper examines how new physics and deviations in the top-quark-Higgs coupling affect one-loop Higgs processes, finding current data allows significant deviations from the standard model.

Contribution

It analyzes the impact of new physics on one-loop Higgs couplings and constrains the top-Higgs Yukawa coupling deviations using current experimental data.

Findings

Current data allows up to 20% deviation in the top-Higgs coupling without new physics.

Introducing a color octet electroweak doublet extends the scalar sector, permitting up to 40% deviation.

Constraints on top-Higgs coupling deviations depend on the presence of new particles in loops.

Abstract

After the discovery of a 126 GeV state at the LHC it is imperative to establish whether this particle really is the Higgs boson of the standard model. The early measurements have not yet pinpointed any of the Higgs couplings to fermions, the Yukawa couplings of the standard model. In this paper we study the values of the top-quark-Higgs coupling, $g_{ht\bar{t}}$, that are still allowed by the one-loop couplings of the Higgs to two gluons or two photons. We first assume that both the gluon fusion production of the Higgs and its decay into two photons proceed through loops with standard model particles only, albeit with an arbitrary top-Higgs coupling. We find that the current Higgs data still allows for 20% deviations in $g_{ht\bar{t}}$ from its standard model value. We then investigate the effect of new particles contributing to the effective one-loop couplings. Specifically we consider a color octet electroweak doublet extension of the scalar sector and find that in this case $g_{ht\bar{t}}$ is allowed to deviate by 40% from its standard model value by the current data.