# The electro-weak couplings of the top and bottom quarks -- global fit and future prospects

## TL;DR

This paper performs a comprehensive global analysis of the electroweak couplings of top and bottom quarks using LHC and LEP/SLC data, providing current bounds and future projections for collider experiments.

## Contribution

It derives combined bounds on effective field theory operators affecting top and bottom quark couplings, including projections for future collider sensitivities.

## Key findings

- Current bounds tightly constrain left-handed couplings.
- Future colliders can improve bounds by factors of 1 to 5.
- e+e- colliders above top threshold can enhance sensitivity by 1-2 orders of magnitude.

## Abstract

We evaluate the implications of LHC and LEP/SLC measurements for the electro-weak couplings of the top and bottom quarks. We derive global bounds on the Wilson coefficients of ten two-fermion operators in an effective field theory description. The combination of hadron collider data with $Z$-pole measurements is found to yield tight limits on the operator coefficients that modify the left-handed couplings of the bottom and top quark to the $Z$ boson. We also present projections for the high-luminosity phase of the LHC and for future electron-positron colliders. The bounds on the operator coefficients are expected to improve substantially during the remaining LHC programme, by factors of $1$ to $5$ if systematic uncertainties are scaled as statistical ones. The operation of an $e^+e^-$ collider at a center-of-mass energy above the top-quark pair production threshold is expected to further improve the bounds by one to two orders of magnitude. The combination of measurements in $pp$ and $e^+e^-$ collisions allows for a percent-level determination of the top-quark Yukawa coupling, that is robust in a global fit.