Composite top partners in exotic colour representations

TL;DR

This paper explores the phenomenology of colour-sextet fermionic resonances in composite Higgs models, analyzing their decay patterns and current LHC constraints, and projecting future discovery potential.

Contribution

It systematically studies colour-sextet top partners in minimal models, deriving their decay modes and reinterpretation of collider searches to set bounds.

Findings

Current LHC data exclude sextet masses up to 2-2.5 TeV.

Sextets mainly decay via coloured pseudo-Nambu-Goldstone bosons.

HL-LHC could reach sensitivities close to 3 TeV.

Abstract

Composite Higgs models with partial compositeness generically predict coloured fermionic resonances associated with the strong dynamics responsible for electroweak symmetry breaking. While most phenomenological studies have focused on colour-triplet and colour-octet top partners, several UV-complete hypercolour constructions also contain fermionic colour sextets. We present a systematic study of these states in the minimal model classes where they arise, constructing the relevant low-energy interactions and deriving their characteristic decay patterns. The sextets predominantly decay through coloured pseudo-Nambu-Goldstone bosons, leading to top-rich final states, while additional channels with $b$-jets and missing transverse energy can be important. We reinterpret existing ATLAS and CMS searches for high-multiplicity final states to derive the dedicated constraints on these resonances. For the benchmark spectra considered, current LHC data exclude individual sextet components up to masses in the $2-2.5$ TeV regime, with stronger bounds when the full sextet multiplet is included, while conservative extrapolations to the HL-LHC indicate a reach close to $3$ TeV. Our results therefore show that colour-sextet fermions provide a powerful and largely unexplored probe of composite Higgs models with partial compositeness.