# Vector-like Fermions and Higgs Effective Field Theory Revisited

## TL;DR

This paper performs a comprehensive analysis of vector-like quark models, linking experimental constraints with Higgs physics and EFT parameters, revealing significant restrictions on these models.

## Contribution

It provides a global fit of VLQ model parameters using precision data, explores their connection to Higgs and Zb interactions, and constrains these models within an EFT framework.

## Key findings

- VLQ models are highly constrained by current data
- Analytical formulas for S and T parameters are provided
- Connection between Zb interactions and Higgs physics is analyzed

## Abstract

Heavy vector-like quarks (VLQs) appear in many models of beyond the Standard Model physics. Direct experimental searches require these new quarks to be heavy, $\gsim$ 800-1000 GeV. We perform a global fit of the parameters of simple VLQ models in minimal representations of $SU(2)_L$ to precision data and Higgs rates. An interesting connection between anomalous $Z b {\overline {b}}$ interactions and Higgs physics in VLQ models is discussed. Finally, we present our analysis in an effective field theory (EFT) framework and show that the parameters of VLQ models are already highly constrained. Exact and approximate analytical formulas for the $S$ and $T$ parameters in the VLQ models we consider are posted at https://quark.phy.bnl.gov/Digital_Data_Archive/dawson/vlq_17/ as Mathematica files.