Exotic decays of top partners: mind the search gap

TL;DR

This paper explores exotic decay modes of top partners in composite Higgs models, revealing that current searches may miss these decays and that lighter top partners are still viable.

Contribution

It introduces a scenario where top partners decay into a pseudo-scalar, highlighting a search gap and showing that existing constraints are weaker for these exotic decays.

Findings

Constraints on top partner mass are significantly weakened for exotic decay modes.

Top partners as light as 400 GeV remain allowed under current bounds.

Exotic decay channels could evade standard search strategies.

Abstract

Many standard model extensions, including composite Goldstone Higgs models, predict vector-like fermionic top-partners at the TeV scale. The intensive search programmes by ATLAS and CMS focus on decays into a 3$^{\rm rd}$ generation quark and an electroweak boson ($W,Z,h$). However, underlying models of partial compositeness contain additional states that give rise to exotic top partner decays. We consider a well-motivated scenario in which a charge-$2/3$ top-partner decays into a pseudo-scalar, $T\rightarrow t\ a$, with $a\rightarrow gg \mbox{ or } b\bar{b}$ dominating below the $t\bar{t}$ threshold. We show that the constraints on the top partner mass from QCD pair production are substantially weakened, still allowing a top partner mass as light as $400$ GeV.