# Hunting for Vectorlike Quarks

## TL;DR

This paper investigates decay patterns of vectorlike quarks in extended models, highlighting how their branching ratios depend on Yukawa couplings and Higgs sector parameters, with implications for collider signatures.

## Contribution

It provides a comprehensive analysis of decay modes and branching ratios of vectorlike quarks, including the impact of Higgs couplings and deviations from Goldstone boson equivalence limit patterns.

## Key findings

- Decays into heavy Higgs bosons can dominate, reaching nearly 100% in certain scenarios.
- Pair production leads to distinctive multi-top and multi-bottom final states.
- Decay patterns follow the Goldstone boson equivalence limit, with possible significant deviations.

## Abstract

We analyze decays of vectorlike quarks in extensions of the standard model and a two Higgs doublet model. We identify several typical patterns of branching ratios of the lightest new up-type quark, $t_4$, and down-type quark, $b_4$, depending on the structure of Yukawa couplings that mix the vectorlike and standard model quarks (we assume only mixing with the third generation) and also on their doublet or singlet nature. We find that decays into heavy neutral or charged Higgs bosons, when kinematically open, can easily dominate and even be close to 100\%: $b_4\to H b$ at medium to large $\tan \beta$, $t_4\to H t$ at small $\tan \beta$ and $b_4\to H^\pm t$, $t_4\to H^\pm b$ at both large and small $\tan \beta$. The pair production of vectorlike quarks leads to $6 t$, $4t 2b$, $2t4b$ and $6b$ final states. The decay modes into $W$, $Z$ and $h$ follow the pattern expected from the Goldstone boson equivalence limit that we generalize to scenarios with all possible couplings. We also discuss in detail the structure of Yukawa couplings required to significantly deviate from the pattern characteristic of the Goldstone boson equivalence limit that can result in essentially arbitrary branching ratios.