One light composite Higgs boson facing electroweak precision tests

TL;DR

This paper analyzes electroweak precision constraints on a minimal composite Higgs model based on SO(5)/SO(4) symmetry breaking, showing it can satisfy constraints with specific top quark compositeness scenarios, predicting testable LHC signatures.

Contribution

It provides a detailed analytical and numerical study of electroweak bounds on a minimal composite Higgs model, highlighting the role of top quark compositeness and predicting potential LHC signals.

Findings

Electroweak constraints can be satisfied with a fully composite left-handed top quark.

A light singlet top partner can evade flavor physics constraints and be detectable at the LHC.

The model predicts a spectrum accessible to current collider experiments.

Abstract

We study analytically and numerically the bounds imposed by the electroweak precision tests on a minimal composite Higgs model. The model is based on spontaneous SO(5)/SO(4) breaking, so that an approximate custodial symmetry is preserved. The Higgs arises as a pseudo-Goldstone boson at a scale below the electroweak symmetry breaking scale. We show that one can satisfy the electroweak precision constraints without much fine-tuning. This is the case if the left-handed top quark is fully composite, which gives a mass spectrum within the reach of the LHC. However a composite top quark is strongly disfavoured by flavour physics. The alternative is to have a singlet top partner at a scale much lighter than the rest of the composite fermions. In this case the top partner would be light enough to be produced significantly at the LHC.