Singlets in composite Higgs models in light of the LHC 750 GeV diphoton excess

Abstract

Models of compositeness can successfully address the origin of the Higgs boson, as a pseudo-Nambu-Goldstone boson (pNGB) of a spontaneously broken global symmetry, and flavor physics via the partial compositeness mechanism. If the dynamics is generated by a confining gauge group with fermionic matter content, there exists only a finite set of models that have the correct properties to account for the Higgs and top partners at the same time. In this paper, we explore the theory space of this class of models; remarkably, all of them contain---beyond the pNGB Higgs---a pNGB singlet, $a$, which couples to Standard Model gauge bosons via Wess-Zumino-Witten interactions, thus providing naturally a resonance in the diboson at the LHC. With the assumption that the recently reported diphoton excess at 750 GeV at the LHC arises from the $a$ resonance, we propose a generic approach on how to delineate the best candidate for composite Higgs models with top partners. We find that constraints from other diboson searches severely reduce the theory space of the models under consideration. For the models which can explain the diphoton excess, we make precise and testable predictions for the width and other diboson resonance searches.