<p>Axionlike 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, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mi>Z</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>−</mo></msup></math>, dijet, and vector-boson-fusion (VBF) 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 modify collider observables. Using Run-2 LHC measurements, we extract bounds on the Wilson coefficients <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msub><mi>c</mi><mover accent="true"><mi>G</mi><mo stretchy="false">˜</mo></mover></msub><mo>,</mo><msub><mi>c</mi><mover accent="true"><mi>W</mi><mo stretchy="false">˜</mo></mover></msub><mo>,</mo><msub><mi>c</mi><mover accent="true"><mi>B</mi><mo stretchy="false">˜</mo></mover></msub><mo stretchy="false">)</mo></math> that parametrize gluonic and electroweak ALP interactions. Our results show that the dijet channel dominates the sensitivity to ALP couplings and determines the limits on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>c</mi><mover accent="true"><mi>G</mi><mo stretchy="false">˜</mo></mover></msub></math>, while diboson and VBF processes provide complementary constraints on the electroweak couplings. We further assess the validity of the effective field theory expansion at the multi-TeV scales probed by 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 measurements.</p>

Czechia

Fabian Esser

Spain

Alexandre Salas-Bernárdez

Veronica Sanz

United Kingdom

Maria Ubiali

Global analysis of ALP-mediated multiboson production at the LHC

We study axion-like particles (ALPs) whose dominant interactions are with gluons and third-generation quarks, and whose couplings to light Standard Model (SM) particles arise at one loop. These loop-induced effects lead to ALP decays and production channels that can be probed at the LHC, even when tree-level couplings are absent. Using an effective field theory (EFT) description that includes momentum-dependent corrections from radiative effects, we reinterpret a wide range of LHC measurements via the Contur framework to derive model-independent constraints on the ALP parameter space. We show that LHC data place meaningful bounds in the plane of effective couplings $$ {c}_t^0/{f}_a $$ and $$ {c}_{\overset{\sim }{G}}^0/{f}_a $$ , and that these limits are sensitive to the UV origin of the ALP-top and ALP-gluon couplings. We discuss representative scenarios where either $$ {c}_t^0 $$ or $$ {c}_{\overset{\sim }{G}}^0 $$ vanishes at the matching scale, and highlight the role of EFT running and mixing in generating observable signals. We also assess the domain of validity of the EFT approach by comparing the typical momentum transfer $$ \sqrt{\hat{s}} $$ in sensitive regions to the underlying scale $\textit{f}$ . Our results demonstrate the power of loop-aware EFT reinterpretation of SM measurements in probing otherwise elusive ALP scenarios. The framework presented here can be readily extended to include couplings to other fermions and to accommodate ALP decay or long-lived signatures.

Jon Butterworth

Matthew Cullingworth

Joseph Egan

Probing the coupling of axions to tops and gluons with LHC measurements

We explore the use of symbolic regression to derive compact analytical expressions for angular observables relevant to electroweak boson production at the Large Hadron Collider (LHC). Focusing on the angular coefficients that govern the decay distributions of $\textit{W}$ and $\textit{Z}$ bosons, we investigate whether symbolic models can well approximate these quantities, typically computed via computationally costly numerical procedures, with high fidelity and interpretability. Using the PySR package, we first validate the approach in controlled settings, namely in angular distributions in lepton-lepton collisions in QED and in leading-order Drell-Yan production at the LHC. We then apply symbolic regression to extract closed-form expressions for the angular coefficients $\textit{A}$ as functions of transverse momentum, rapidity, and invariant mass, using next-to-leading order simulations of $\textit{pp}$ → $\textit{ℓ}$ $\textit{ℓ}$ events. Our results demonstrate that symbolic regression can produce accurate and generalisable expressions that match Monte Carlo predictions within uncertainties, while preserving interpretability and providing insight into the kinematic dependence of angular observables.

Josh Bendavid

Daniel Conde

Italy

Manuel Morales-Alvarado

Angular coefficients from interpretable machine learning with symbolic regression

<p>We present a novel strategy to uncover indirect signs of new physics in collider data using the standard model effective field theory (SMEFT) framework, offering notably improved sensitivity compared to traditional global analyses. Our approach leverages genetic algorithms to efficiently navigate the high-dimensional space of operator subsets, identifying deformations that improve agreement with data without relying on prior ultraviolet (UV) assumptions. This enables the systematic detection of SMEFT scenarios that outperform the standard model in explaining observed deviations. We validate the approach on current large hadron collider and large electron-positron collider measurements, perform closure tests with injected UV signals, and assess performance under high-luminosity projections. The algorithm successfully recovers relevant operator subsets and highlights directions in parameter space where deviations are most likely to emerge. Our results demonstrate the potential of SMEFT-based discovery searches driven by model selection, providing a scalable framework for future data analyses.</p>

Martin Hirsch

Luca Mantani

Data-Driven Discovery Strategy for Standard Model Effective Field Theory Searches

The Standard Model Effective Field Theory (SMEFT) offers a systematic approach to study potential deviations from the Standard Model (SM) through higher-dimensional operators that encapsulate new physics effects. In this work, we analyze flavour-blind SMEFT contributions to flavour observables and assess their interplay with high-energy measurements from LEP and LHC. We perform global fits combining LEP precision data, flavour observables from rare B-meson decays, and LHC diboson measurements, revealing how the inclusion of different datasets breaks parameter degeneracies and enhances the sensitivity to SMEFT coefficients. Our study demonstrates that low-energy flavour observables provide reliable constraints even in flavour-blind scenarios, while high-energy measurements can be subject to EFT validity concerns due to kinematic growth. We investigate the impact of renormalization group evolution (RGE) and operator mixing across energy scales, highlighting the complementary nature of low- and high-energy datasets. The results emphasize the importance of flavour observables as robust probes of new physics and underline the necessity of global fits to avoid potential biases from limited datasets. Finally, we discuss the implications of our findings for the interpretation of global SMEFT analyses based on high-energy collider data, comparing UV models that contribute to SMEFT at tree- and loop-level.

Probing the flavour-blind SMEFT: EFT validity and the interplay of energy scales

We present a new study on the Gravity-Mediated Dark Matter (GMDM) scenario, where interactions between dark matter (DM) and the Standard Model are mediated by spin-two particles. Expanding on this established framework, we explore a novel regime characterized by a low reheating temperature that offers an alternative to the conventional thermal relic paradigm. This approach opens new possibilities for understanding the dynamics of the dark sector, encompassing both the dark matter particles (fermion, scalar and vector) and the spin-two mediators. Our analysis examines the constraints imposed by the relic abundance of DM, collider experiments, and direct detection searches, spanning a wide mass range for the dark sector, from very light to extremely heavy states. This work opens new possibilities for the phenomenology of GMDM.

South Korea

Hyun Lee

Myeonghun Park

Gravity-Mediated Dark Matter at a low reheating temperature

Searches for anomalous neutral triple gauge boson couplings (NTGCs) provide important tests for the gauge structure of the standard model. At the LHC, NTGCs are searched for via the process $\textit{pp}$ → $\textit{ZZ}$ → 4$\textit{l}$, where the two $\textit{Z}$-bosons are on-shell. In this paper, we discuss how the same process can occur through tree-level diagrams just adding a vector-like quark (VLQ) to the standard model. Since NTGCs are generated in standard model effective theory (SMEFT) only at 1-loop order, vector like quarks could be an important alternative interpretation to, and background for, NTGC searches. Here, we construct a simple example model, discuss low-energy constraints and estimate current and future sensitivities on the model parameters from $\textit{pp}$ → $\textit{ZZ}$ → 4$\textit{l}$ searches.

Ricardo Cepedello

Faking ZZZ vertices at the LHC

A correction to this paper has been published: https://doi.org/10.1007/JHEP07(2024)275

Erratum to: Fermionic UV models for neutral triple gauge boson vertices

Due to the pseudo-scalar nature of the axion-like particle (ALP), the CP-conserving production of two Higgs bosons via the ALP necessarily involves an additional Z or γ boson. We examine the existing constraints from di-Higgs searches at Run 2 of the LHC and find that, despite the presence of extra objects in the final state, these searches are sensitive to a combination of ALP couplings to gluons and three-bosons in the TeV scale range. Additionally, we propose a specialized search strategy incorporating an energetic leptonic Z boson. This refined ALP-induced production process would allow for the identification of the h h → 4 b-jet final state and could potentially probe the TeV scale using data from Run 2 of the LHC. This production process can also occur through a coupling between the top quark and the ALP. We translate the current constraints on di-Higgs production into new limits on the ALP-top coupling.

Germany

Maeve Madigan

Di-Higgs production via axion-like particles

Searches for anomalous neutral triple gauge boson couplings (NTGCs) provide important tests for the gauge structure of the standard model. In SMEFT (“standard model effective field theory”) NTGCs appear only at the level of dimension-8 operators. While the phenomenology of these operators has been discussed extensively in the literature, renormalizable UV models that can generate these operators are scarce. In this work, we study a variety of extensions of the SM with heavy fermions and calculate their matching to d = 8 NTGC operators. We point out that the complete matching of UV models requires four different CP-conserving d = 8 operators and that the single CPC d = 8 operator, most commonly used by the experimental collaborations, does not describe all possible NTGC form factors. Despite stringent experimental constraints on NTGCs, limits on the scale of UV models are relatively weak, because their contributions are doubly suppressed (being d = 8 and 1-loop). We suggest a series of benchmark UV scenarios suitable for interpreting searches for NTGCs in the upcoming LHC runs, obtain their current limits and provide estimates for the expected sensitivity of the high-luminosity LHC.