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.
Highlights
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 paper we explored the relation which, in a broad class of composite Higgs models, links a light Higgs boson to the presence of light resonances coming from the new strong sector of the theory
The class of models we focused on are the ones based on the symmetry pattern SO(5)/SO(4) and in which the fermionic resonances come in the fundamental representation of SO(5)
Summary
If the Higgs is a pNGB its potential, and in particular its mass mH , can only be generated through the breaking of the Goldstone symmetry. It is very reasonable to expect a tight relation among the Higgs mass and the fermionic sector of the theory which is responsible for the generation of yt. The mixings ensure the communication among the strong sector, which is invariant under the Goldstone symmetry, and the elementary sector which is not They break the symmetry and allow for the generation of the Higgs mass. (2.3) and (2.5) that making both mT and mT small at the same time produces a quadratic decrease of y2 and of mH This behavior is never found in the explicit models we will investigate the effect is always linear. If both masses become small one power of mT,T in eqs. (2.3) and (2.5) is compensated by Y∗ and the effect remains linear
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