Low-Energy Constraints on New Physics Revisited

TL;DR

The paper develops a unified EFT framework to constrain non-SM gauge-boson self-interactions using precision electroweak data, comparing linear (light-Higgs) and nonlinear (no-Higgs) realizations of electroweak symmetry breaking. It expresses new-physics effects through running effective charges and a $Zb\overline{b}$ vertex form factor, enabling a global $\chi^2$ analysis that yields bounds on dimension-6 linear operators and on chiral Lagrangian coefficients. The results show that tree-level operators in the linear model are tightly constrained, while loop-induced operators are more model-dependent; in the nonlinear model, the coefficients $\alpha_1$, $\beta_1$, and $\alpha_8$ are constrained with notable correlations, and explicit scalar or fermion-dynamics scenarios illustrate how the bounds translate into physical parameter space. Overall, the work provides a comprehensive, gauge-invariant method to translate electroweak precision data into meaningful limits on non-SM gauge interactions, with clear implications for current and future collider experiments.

Abstract

It is possible to place constraints on non-Standard-Model gauge-boson self-couplings and other new physics by studying their one-loop contributions to precisely measured observables. We extend previous analyses which constrain such nonstandard couplings, and we present the results in a compact and transparent form. Particular attention is given to comparing results for the light-Higgs scenario, where nonstandard effects are parameterized by an effective Lagrangian with a linear realization of the electroweak symmetry breaking sector, and the heavy-Higgs/strongly interacting scenario, described by the electroweak chiral Lagrangian. The constraints on nonstandard gauge-boson self-couplings which are obtained from a global analysis of low-energy data and LEP/SLC measurements on the Z pole are updated and improved from previous studies. Replaced version: tables and figures of Section VIb recalculated. There were roundoff problems, especially in Fig. 8. Text unchanged.

Figures (10)

• Figure 1: Higher-order contributions to the $V_1^\mu V_2^\nu$ two-point-functions; $V_1V_2$ denotes $\gamma\gamma$, $\gamma Z$, $ZZ$ or $WW$. Generically the 'blob' may represent a contact term, a 'bubble' or a 'tadpole'.
• Figure 2: Higher-order contributions to the $Vf_1f_2$ vertex where $V = \gamma$, $Z$ or $W$. Generically the 'blob' in (a) denotes a large variety of graphs. However, for the new-physics contributions which we discuss, all contributions arise from graphs of type (b).
• Figure 3: Constraints at the 95% confidence level in the $f_{DW}$--$f_{DB}$ plane with $f_{WW} = 20\lambda_If_{DW}$ and $f_{BB} = 20\lambda_If_{DB}$ for $\Lambda = 1$ TeV, $m_t = 175$ GeV and $m_H = 200$ GeV. The solid, dashed and dotted curves correspond to $\lambda_I =$ 0.1, 1 and 5 respectively.
• Figure 4: Constraints on $f_{WWW}$, $f_{W}$ and $f_{B}$ at the 95% confidence level for $\Lambda =$ 1 TeV and $m_t =$ 175 GeV.
• Figure 5: Constraints on $\Delta\kappa_\gamma$, $\Delta\kappa_Z$ and $\lambda = \lambda_\gamma = \lambda_Z$ at the 95% confidence level assuming the relations of Eqns. \ref{['hisz-relations']} with $\Lambda =$ 1 TeV and $m_t =$ 175 GeV.