Anomalous gauge couplings from composite Higgs and warped extra dimensions

TL;DR

The work addresses how new physics at the TeV scale can imprint anomalous gauge couplings in the Standard Model through two well-motivated UV frameworks: composite Higgs models and warped extra dimensions (AdS$_5$). It formulates a two-tier EFT with $\mathcal{L}_{\rm eff}=\mathcal{L}_{\rm SM}+\mathcal{L}_{(6)}+\mathcal{L}_{(8)}$, and computes the loop-induced pure-gauge contributions $\mathcal{L}^{\partial}$ using the heat-kernel method, providing model-independent expressions in terms of heavy-state quantum numbers. In composite Higgs scenarios, exotics in the top-partner sector typically dominate anomalous couplings, offering distinctive patterns that could signal the global symmetry structure; in the holographic AdS$_5$ view, KK gravitons, KK gauge modes, and radion dynamics shape the same operator classes, with the relevance set by gauge-field localization and brane kinetic terms. The analysis derives updated bounds from Higgs and electroweak precision data on KK masses and radion parameters, and demonstrates that forward proton detectors at the LHC can probe KK gravitons and related couplings in the multi-TeV range, complementing indirect precision constraints. Overall, the paper provides a cohesive framework linking UV completions to measurable AGCs, offering concrete predictions and experimental avenues for testing these BSM scenarios.

Abstract

We examine trilinear and quartic anomalous gauge couplings (AGCs) generated in composite Higgs models and models with warped extra dimensions. We first revisit the SU(2)_L x U(1)_Y effective Lagrangian and derive the charged and two-photon neutral AGCs. We derive the general perturbative contributions to the pure field-strength operators from spin 0, 1/2, 1 resonances by means of the heat kernel method. In the composite Higgs framework, we derive the pattern of expected deviations from typical SO(N) embeddings of the light composite top partner. We then study a generic warped extra dimension framework with AdS_5 background, recasting in few parameters the features of models relevant for AGCs. We also present a detailed study of the latest bounds from electroweak and Higgs precision observables, with and without brane kinetic terms. For vanishing brane kinetic terms, we find that the S and T parameters exclude KK gauge modes of the RS custodial [non-custodial] scenario below 7.7 [14.7] TeV, for a brane Higgs and below 6.6 [8.1] TeV for a Pseudo Nambu-Goldstone Higgs, at 95% CL. These constraints can be relaxed in presence of brane kinetic terms. The leading AGCs are probing the KK gravitons and the KK modes of bulk gauge fields in parts of the parameter space. In these scenarios, the future CMS and ATLAS forward proton detectors could be sensitive to the effect of KK gravitons in the multi-TeV mass range.

Figures (2)

• Figure 1: Electroweak, Higgs and gauge precision bounds for $\tilde{k}=3\, \textrm{TeV}$. The regions excluded at $95\%$ CL are shown in blue, the allowed regions are shown in white. The $S,T$ limit is shown in dark, the $a_V$ limit is shown in dark blue and in dashed lines when $a_W\neq a_Z$, and the $\kappa_3$ limit is shown in purple. Are also displayed extrapolated limits from more stringent constraints $a_{W,Z}>0.99$, $|\kappa_3|<0.01$. The red point denotes the case of vanishing brane kinetic terms. Left and right panels respectively correspond to non-custodial and custodial cases for a pNGB Higgs ($\nu=0$).
• Figure 2: Limits and expected reach in the non-custodial (left) and custodial (right) pNGB Higgs ($\nu=0$) scenarios. The reach of $\zeta_2$ (red) and $\eta_1^W$ (green) from KK gravitons with $\kappa=2$ are shown for sensitivities $\zeta^\gamma_2=(10^{-13},\,10^{-14},\,10^{-15}~\textrm{GeV}^{-4})$ and $\eta^W_1=(10^{-9},\,10^{-10},\,10^{-11}~\textrm{GeV}^{-2})$, from bottom to top. Color code for other limits is the same as in Fig. \ref{['fig:STplot']}.