A global analysis of ALP-mediated multiboson production at the LHC

TL;DR

This work develops a linear ALP EFT with bosonic dimension-five couplings and analyzes ALP-mediated, off-shell multiboson production at the LHC. By combining Run-2 measurements across diphoton, ZZ, WW, dijet, and VBF channels, the authors perform a global three-parameter fit to $(c_G,c_W,c_B)$ at $f_a=1$ TeV, carefully accounting for correlations and EFT validity. The dijet channel dominantly constrains the gluonic coupling $c_G$, while diboson and VBF channels constrain the electroweak couplings $c_W$ and $c_B$, respectively, with their interplay closing flat directions in the parameter space. EFT-robustness checks indicate the bounds lie within NDA-consistent regions for the probed kinematics, and the study highlights significant prospects for HL-LHC to improve sensitivity and for future three-boson channels to provide complementary information.

Abstract

Axion-like particles (ALPs) provide a well-motivated framework for physics beyond the Standard Model, coupling to gauge bosons through dimension-five operators protected by an approximate shift symmetry. At the LHC, such interactions lead to distinctive signatures in multiboson production, where the ALP appears as an off-shell mediator rather than a narrow resonance. In this work, we present the first global analysis of ALP-mediated multiboson processes, combining measurements of diphoton, ZZ, $W^+ W^-$, dijet, and vector-boson-fusion final states. On the theory side, motivated from a UV perspective, we assume that the ALP couples only to the gauge sector of the SM, and classify the ALP-multiboson vertices that directly govern collider observables. Our results show that the dijet channel dominates the sensitivity to ALP couplings and determines the limits on $c_{\tilde{G}}$, while diboson and VBF processes provide complementary constraints on the electroweak couplings. We further assess the validity of the EFT expansion given the multi-TeV scales probed in the data. This global study provides the most comprehensive picture to date of ALP-gauge interactions from multiboson production at the LHC, and highlights the opportunities for significant improvements with future high-luminosity datasets.

Figures (16)

• Figure 1: Representative anomaly triangle generating a $a\,F\tilde{F}$ term in the effective Lagrangian with heavy fermions $\Psi$.
• Figure 2: Schematic parton-level topologies for multiboson production. Left: SM continuum (box/topology example). Right: virtual ALP exchange with no resonant cut. Our analysis targets this non-resonant regime). Here $V,V'\in\{g,\gamma,Z,W\}$.
• Figure 3: Diphoton invariant-mass distribution. The signal is shown for $c_{\tilde{G}}=1$, $c_{\tilde{W}}=1$ and $c_{\tilde{B}}=0$, compared to ATLAS data ATLAS:2021mbt and the SM prediction from SHERPA.
• Figure 4: Differential cross section for the four-lepton invariant mass $m_{4\ell}$ in $ZZ$ production. The signal is shown for $c_{\tilde{G}}=1$, $c_{\tilde{W}}=1$, $c_{\tilde{B}}=0$, compared to ATLAS data and the SM prediction ATLAS:2023dew.
• Figure 5: Differential cross section in the $WW$ final state as a function of the diboson invariant mass. The signal is shown for $c_{\tilde{G}}=1$, $c_{\tilde{W}}=1$ and $c_{\tilde{B}}=0$, compared to the ATLAS data and the SM background simulation in ATLAS:2019rob.