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Minimal Composite Higgs Model with Light Bosons

Bogdan A. Dobrescu

TL;DR

This paper develops a minimal composite Higgs framework in which the Higgs arises as a bound state from top-sector dynamics augmented by a vector-like quark χ. By extending the Higgs sector to two doublets and two singlets and enforcing a compositeness condition at a scale M_c, it analyzes the resulting scalar spectrum, predicting a light CP-even Higgs h^0 and, depending on symmetry breaking, at most one light CP-odd state (a composite axion). It highlights the potential dominance of h^0 decays into axion pairs and discusses the implications for collider searches, as well as constraints from astrophysical and cosmological observations on the composite axion. The model yields a decoupling limit where low-energy phenomenology resembles the SM but with characteristic large Higgs self-couplings and distinctive decay channels that could reveal the underlying strong dynamics. Comparisons with the MSSM emphasize different UV completions and signatures, offering testable predictions for future high-energy experiments.

Abstract

We analyze a composite Higgs model with the minimal content that allows a light Standard-Model-like Higgs boson, potentially just above the current LEP limit. The Higgs boson is a bound state made up of the top quark and a heavy vector-like quark. The model predicts that only one other bound state may be lighter than the electroweak scale, namely a CP-odd neutral scalar. Several other composite scalars are expected to have masses in the TeV range. If the Higgs decay into a pair of CP-odd scalars is kinematically open, then this decay mode is dominant, with important implications for Higgs searches. The lower bound on the CP-odd scalar mass is loose, in some cases as low as $\sim$ 100 MeV, being set only by astrophysical constraints.

Minimal Composite Higgs Model with Light Bosons

TL;DR

This paper develops a minimal composite Higgs framework in which the Higgs arises as a bound state from top-sector dynamics augmented by a vector-like quark χ. By extending the Higgs sector to two doublets and two singlets and enforcing a compositeness condition at a scale M_c, it analyzes the resulting scalar spectrum, predicting a light CP-even Higgs h^0 and, depending on symmetry breaking, at most one light CP-odd state (a composite axion). It highlights the potential dominance of h^0 decays into axion pairs and discusses the implications for collider searches, as well as constraints from astrophysical and cosmological observations on the composite axion. The model yields a decoupling limit where low-energy phenomenology resembles the SM but with characteristic large Higgs self-couplings and distinctive decay channels that could reveal the underlying strong dynamics. Comparisons with the MSSM emphasize different UV completions and signatures, offering testable predictions for future high-energy experiments.

Abstract

We analyze a composite Higgs model with the minimal content that allows a light Standard-Model-like Higgs boson, potentially just above the current LEP limit. The Higgs boson is a bound state made up of the top quark and a heavy vector-like quark. The model predicts that only one other bound state may be lighter than the electroweak scale, namely a CP-odd neutral scalar. Several other composite scalars are expected to have masses in the TeV range. If the Higgs decay into a pair of CP-odd scalars is kinematically open, then this decay mode is dominant, with important implications for Higgs searches. The lower bound on the CP-odd scalar mass is loose, in some cases as low as 100 MeV, being set only by astrophysical constraints.

Paper Structure

This paper contains 15 sections, 57 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Ingredients of a Minimal Composite Higgs Model
  3. The vector-like quark
  4. Extending the Higgs sector
  5. Candidates for physics above the compositeness scale
  6. The Two-Doublet-Two-Singlet Higgs Sector
  7. CP-odd neutral scalars
  8. CP-even neutral scalars
  9. Light Boson Spectrum
  10. Standard Model in the decoupling limit
  11. Light top-axion
  12. Light $\chi$-axion
  13. Composite Scalar Couplings to Quarks and Leptons
  14. Bounds on the Composite Axion
  15. Discussion

Figures (4)

  • Figure 1: Large-$N_c$ contributions to the Higgs doublet self-energy and quartic coupling.
  • Figure 2: Tadpole terms for the electroweak singlet scalars.
  • Figure 3: One-loop contribution of the heavy scalars to the trilinear coupling of the Higgs boson to composite-axion pairs.
  • Figure 4: Leading-$N_c$ contribution to the Yukawa couplings of the Standard Model fermions.