Light Top Partners for a Light Composite Higgs

TL;DR

This paper demonstrates that light top partners are a natural and essential feature of composite Higgs models, with their presence strongly correlated to the Higgs mass, and discusses implications for LHC searches.

Contribution

It provides a generic analytical and numerical analysis showing the necessity of light top partners in composite Higgs models, confirmed within the Discrete Composite Higgs Model framework.

Findings

Light top partners are correlated with a realistic Higgs mass.

LHC searches already constrain top partner masses, excluding some parameter space.

The absence of light top partners would challenge the composite Higgs scenario.

Abstract

Anomalously light fermionic partners of the top quark often appear in explicit constructions, such as the 5d holographic models, where the Higgs is a light composite pseudo Nambu-Goldstone boson and its potential is generated radiatively by top quark loops. We show that this is due to a structural correlation among the mass of the partners and the one of the Higgs boson. Because of this correlation, the presence of light partners could be essential to obtain a realistic Higgs mass. We quantitatively confirm this generic prediction, which applies to a broad class of composite Higgs models, by studying the simplest calculable framework with a composite Higgs, the Discrete Composite Higgs Model. In this setup we show analytically that the requirement of a light enough Higgs strongly constraints the fermionic spectrum and makes the light partners appear. The light top partners thus provide the most promising manifestation of the composite Higgs scenario at the LHC. Conversely, the lack of observation of these states can put strong restrictions on the parameter space of the model. A simple analysis of the 7-TeV LHC searches presently available already gives some non-trivial constraint. The strongest bound comes from the exclusion of the 5/3-charged partner. Even if no dedicated LHC search exists for this particle, a bound of 611 GeV is derived by adapting the CMS search of bottom-like states in same-sign dileptons.