Light 't Hooft Top Partners

TL;DR

The paper proposes a mechanism where the lightness of top partners in composite Higgs models is explained by matching global 't Hooft anomalies, with explicit models demonstrating controllably small masses.

Contribution

It introduces a novel anomaly-matching mechanism to explain the lightness of top partners in composite Higgs theories.

Findings

Explicit models show composite fermions with top quantum numbers can have small masses controlled by soft breaking.

The anomaly-matching mechanism provides a natural explanation for light top partners.

The approach links top partner mass scale to underlying strong dynamics and anomaly conditions.

Abstract

Vector-like quarks, usually dubbed top partners, are a common presence in composite Higgs models. Being composite objects, their mass is expected to be of the order of their inverse size, that is the condensation scale of the new strong interactions. Light top partners, while not being a generic prediction, are however often considered in phenomenological models. We suggest that their lightness may be due to the matching of global 't Hooft anomalies of the underlying theory. We check this mechanism in explicit models showing that, in one case, composite fermions with the quantum numbers of the top quark obtain a mass which is controlled by a soft breaking term and can be made parametrically small.