E6 inspired composite Higgs model

Abstract

We consider a composite Higgs model embedded into a Grand Unified Theory(GUT) based on the E_6 gauge group. The phenomenological viability of this E_6 inspired composite Higgs model (E6CHM) implies that standard model (SM) elementary fermions with different baryon or lepton number should stem from different 27 representations of E_6. We present a six-dimensional orbifold GUT model in which the E_6 gauge symmetry is broken to the SM gauge group so that the appropriate splitting of the bulk 27-plets takes place. In this model the strongly coupled sector is localised on one of the branes and possesses an SU(6) global symmetry that contains the SU(3)_C\times SU(2)_W\times U(1)_Y subgroup. In this case the approximate gauge coupling unification can be attained if the right-handed top quark is a composite state and the elementary sector involves extra exotic matter beyond the SM which ensures anomaly cancellation. The breakdown of the approximate SU(6) symmetry at low energies in this model results in a set of the pseudo-Nambu-Goldstone states which include a Higgs doublet and scalar colour triplet. We discuss the generation of the masses of the SM fermions in the E6CHM. The presence of the TeV scale vector-like exotic quarks and scalar colour triplet may provide spectacular new physics signals that can be observed at the LHC.