Beyond the Minimal Composite Higgs Model

TL;DR

This paper explores an extension of the composite Higgs model based on SO(6)/SO(5), revealing a richer Higgs spectrum with a light CP-odd scalar that impacts Higgs phenomenology, flavor physics, and potential collider signatures.

Contribution

It introduces the SO(6)/SO(5) composite Higgs model with a CP-odd singlet, analyzing its natural light mass, decay channels, and implications for flavor violation and collider experiments.

Findings

The eta scalar can be naturally light, affecting Higgs decay modes.

The Higgs mass bound can be lowered to 86 GeV due to eta decays.

Eta interactions can induce flavor violation and CP-violation.

Abstract

The Higgs spectrum of the minimal composite Higgs model, based on the SO(5)/SO(4) coset, consists of a unique Higgs doublet whose phenomenology does not differ greatly from the Standard Model (SM). Nevertheless, extensions beyond this minimal coset structure exhibit a richer Higgs spectrum and therefore very different Higgs physics. We explore one of these extensions, the SO(6)/SO(5) model, whose Higgs spectrum contains a CP-odd singlet scalar, eta, in addition to the Higgs doublet. Due to the pseudo-Nambu-Goldstone nature of these Higgs bosons, their physical properties can be derived from symmetry considerations alone. We find that the mass of eta can be naturally light, opening up the possibility that the SM Higgs decays predominantly to the singlet, and therefore lowering the LEP bound on its mass to 86 GeV. We also show that eta can have interesting consequences in flavour-violating processes, as well as induce spontaneous CP-violation in the Higgs sector. The model can also have anomalies, giving rise to interactions between the SM gauge bosons and eta which, if measured at the LHC, would give quantitative information about the structure of the high energy theory.