Effective potential in ultraviolet completions for composite Higgs models

Abstract

We consider a class of composite Higgs models based on asymptotically free SO(d) gauge theories with d odd, with fermions in two irreducible representations, and in which the Higgs field arises as a pseudo-Nambu-Goldstone boson and the top quark is partially composite. The Nambu-Goldstone coset containing the Higgs field, or Higgs coset, is either SU(4)/Sp(4) or SU(5)/SO(5), whereas the top partners live in two-index representations of the relevant flavor group [SU(4) or SU(5)]. In both cases, there is a large number of terms in the most general four-fermion Lagrangian describing the interaction of third-generation quarks with the top partners. We derive the top-induced effective potential for the Higgs coset together with the singlet pseudo-Nambu-Goldstone boson associated with the non-anomalous axial symmetry, to leading order in the couplings between the third-generation quarks and the composite sector. We obtain expressions for the low-energy constants in terms of top-partner two-point functions. We revisit the effective potential of another composite Higgs model that we have studied previously, which is based on an SU(4) gauge theory and provides a different realization of the SU(5)/SO(5) coset. The top partners of this model live in the fundamental representation of SU(5), and, as a result, the effective potential of this model is qualitatively different from the SO(d) gauge theories. We also discuss the role of the isospin-triplet fields contained in the SU(5)/SO(5) coset, and show that, without further constraints on the four-fermion couplings, an expectation value for the Higgs field will trigger the subsequent condensation of an isospin-triplet field.