Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

The Low-Energy Structure of Little Higgs Models

W. Kilian, J. Reuter

TL;DR

The paper develops a complete effective field theory description of Little Higgs models by integrating out heavy vector, scalar, and fermion states to produce a dimension-six operator basis that encapsulates shifts in gauge, Higgs, and fermion couplings. Using the Littlest Higgs model LHmin as a concrete example, it derives the full set of operator coefficients and maps them onto observable effects such as oblique parameters $S$ and $T$ and non-oblique contact interactions, including scenarios with non-universal hypercharge assignments. It demonstrates how precision electroweak data constrain the symmetry-breaking scale $F$ and the vector-boson mixing angles, and discusses the interplay with collider measurements to reconstruct the underlying model. The framework also outlines how anomalous triple-gauge, Higgs, and top-quark couplings arise and how they can be exploited at the LHC and a future Linear Collider to verify the Little Higgs mechanism and the Goldstone-boson nature of the Higgs.

Abstract

The mechanism of electroweak symmetry breaking in Little Higgs Models is analyzed in an effective field theory approach. This enables us to identify observable effects irrespective of the specific structure and content of the heavy degrees of freedom. We parameterize these effects in a common operator basis and present the complete set of anomalous contributions to gauge-boson, Higgs, and fermion couplings. If the hypercharge assignments of the model retain their standard form, electroweak precision data are affected only via the S and T parameters and by contact interactions. As a proof of principle, we apply this formalism to the minimal model and consider the current constraints on the parameter space. Finally, we show how the interplay of measurements at LHC and a Linear Collider could reveal the structure of these models.

The Low-Energy Structure of Little Higgs Models

TL;DR

The paper develops a complete effective field theory description of Little Higgs models by integrating out heavy vector, scalar, and fermion states to produce a dimension-six operator basis that encapsulates shifts in gauge, Higgs, and fermion couplings. Using the Littlest Higgs model LHmin as a concrete example, it derives the full set of operator coefficients and maps them onto observable effects such as oblique parameters and and non-oblique contact interactions, including scenarios with non-universal hypercharge assignments. It demonstrates how precision electroweak data constrain the symmetry-breaking scale and the vector-boson mixing angles, and discusses the interplay with collider measurements to reconstruct the underlying model. The framework also outlines how anomalous triple-gauge, Higgs, and top-quark couplings arise and how they can be exploited at the LHC and a future Linear Collider to verify the Little Higgs mechanism and the Goldstone-boson nature of the Higgs.

Abstract

The mechanism of electroweak symmetry breaking in Little Higgs Models is analyzed in an effective field theory approach. This enables us to identify observable effects irrespective of the specific structure and content of the heavy degrees of freedom. We parameterize these effects in a common operator basis and present the complete set of anomalous contributions to gauge-boson, Higgs, and fermion couplings. If the hypercharge assignments of the model retain their standard form, electroweak precision data are affected only via the S and T parameters and by contact interactions. As a proof of principle, we apply this formalism to the minimal model and consider the current constraints on the parameter space. Finally, we show how the interplay of measurements at LHC and a Linear Collider could reveal the structure of these models.

Paper Structure

This paper contains 25 sections, 129 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Integrating Out Heavy Fields
  3. The Model
  4. Heavy Vector Fields
  5. Heavy Scalars and the Higgs Boson
  6. Heavy Fermions and the Top Quark
  7. Equations of Motion
  8. Custodial-$SU(2)$ Conserving Terms
  9. Custodial-$SU(2)$ Violating Terms
  10. Precision Observables
  11. Oblique Corrections
  12. Non-Universal Hypercharges
  13. Four-Fermion Interactions
  14. Constraints on the Littlest Higgs Model
  15. New Effects
  16. ...and 10 more sections

Figures (1)

  • Figure 1: $ST$ predictions for the Littlest Higgs model with standard $U(1)$ charge assignments LHmin. The shaded ellipses are the $68\,\%$ exclusion contours which follow from the electroweak precision data EWprecPPP03, assuming four different Higgs masses. The hatched areas are the allowed parameter ranges of the Littlest Higgs model for two different values of the scale $F$. The limits from contact interactions have been taken into account.