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Heavy Vectors in Higgs-less models

Riccardo Barbieri, Gino Isidori, Vyacheslav S. Rychkov, Enrico Trincherini

TL;DR

The paper investigates whether one or more heavy spin-1 resonances can replace the Higgs boson to preserve perturbative unitarity and remain compatible with electroweak precision tests. It contrasts a composite triplet-resonance framework with a gauged, deconstructed (N-site) model, deriving their low-energy Lagrangians and computing the full one-loop T parameter to assess S–T correlations. The gauge model cannot saturate EWPT with vector exchanges alone, whereas the composite approach can accommodate both S and T with a relatively light vector under specific couplings (notably F_V ≈ 2G_V and nonzero F_A), yielding a distinctive LHC phenomenology through a narrow V resonance decaying mainly to WZ. The results highlight the necessity of full loop analyses and high-energy form-factor cancellations to maintain calculability, and they provide testable predictions for vector-boson fusion signals at the LHC that could reveal Higgs-less dynamics if realized in nature.

Abstract

One or more heavy spin-1 fields may replace the Higgs boson in keeping perturbative unitarity up to a few TeV. By means of two prototype chiral models for the heavy spin-1 bosons, a "composite" model or a "gauge" model, we discuss if and how the sole exchange of the same fields can also account for the ElectroWeak Precision Tests. While this proves impossible in the gauge model, the composite model hints to a positive solution, which we exploit to constrain the phenomenological properties of the heavy vectors.

Heavy Vectors in Higgs-less models

TL;DR

The paper investigates whether one or more heavy spin-1 resonances can replace the Higgs boson to preserve perturbative unitarity and remain compatible with electroweak precision tests. It contrasts a composite triplet-resonance framework with a gauged, deconstructed (N-site) model, deriving their low-energy Lagrangians and computing the full one-loop T parameter to assess S–T correlations. The gauge model cannot saturate EWPT with vector exchanges alone, whereas the composite approach can accommodate both S and T with a relatively light vector under specific couplings (notably F_V ≈ 2G_V and nonzero F_A), yielding a distinctive LHC phenomenology through a narrow V resonance decaying mainly to WZ. The results highlight the necessity of full loop analyses and high-energy form-factor cancellations to maintain calculability, and they provide testable predictions for vector-boson fusion signals at the LHC that could reveal Higgs-less dynamics if realized in nature.

Abstract

One or more heavy spin-1 fields may replace the Higgs boson in keeping perturbative unitarity up to a few TeV. By means of two prototype chiral models for the heavy spin-1 bosons, a "composite" model or a "gauge" model, we discuss if and how the sole exchange of the same fields can also account for the ElectroWeak Precision Tests. While this proves impossible in the gauge model, the composite model hints to a positive solution, which we exploit to constrain the phenomenological properties of the heavy vectors.

Paper Structure

This paper contains 12 sections, 61 equations, 4 figures.

Table of Contents

  1. Introduction and statement of the problem
  2. The Lagrangian of the composite model
  3. Perturbative unitarity
  4. $T$ at one loop in the composite model
  5. The $SU(2)^{N}$ gauge model
  6. Low-energy limit and comparison with the composite model
  7. One-loop contributions to $T$
  8. Unitarity and EWPT constraints put together
  9. Phenomenology
  10. Summary and conclusions
  11. High momentum behavior of two and three point functions
  12. Heavy spin-1 resonances in QCD

Figures (4)

  • Figure 1: Summary of unitarity and EWPT constraints (at 95% C.L.) in the $(M_{V},G_{V})$ plane (see Sect. \ref{['sect:constr']}).
  • Figure 2: One-loop contributions to $\hat{T}$ generated by $\mathcal{L}^{(2)}$ and by couplings of the heavy vectors at most linear in the heavy fields.
  • Figure 3: One-loop contributions to $\hat{T}$ generated by the $A V \pi$ trilinear couplings.
  • Figure 4: Areas of $S$ and $T$ covered in the composite model for different ranges of the free parameters. The two ellipses denote the experimentally allowed region at 68% and 95% CL. The small cross at negative $T$ values is the $F_{V}=F_{A}=G_{V}=0$ point (infrared logs only).