Axion-like particles are light, pseudoscalar bosons that can couple to photons, gluons, or fermions. Theoretical reviews by Andreas Ringwald at DESY explain how such couplings arise from broken global symmetries and anomaly terms and why they are a target for collider searches. Collider probes are complementary to astrophysical and laboratory searches because colliders can produce ALPs in controlled high-energy interactions and measure specific final states that reveal coupling structure.
Production and detection channels
At colliders ALPs can be produced through photon fusion, gluon fusion, exotic Higgs decays, and in association with vector bosons. Photon fusion produces a clean diphoton resonance when the ALP decays back to photons, a channel actively constrained by the ATLAS Collaboration at CERN and the CMS Collaboration at CERN. Gluon-coupled ALPs can appear as narrow jets or modify multi-jet spectra, while couplings to fermions open decays into leptons or displaced vertices when the ALP is long-lived. Low-mass ALPs that escape the detector produce missing-energy signatures or appear in rare meson decays, a strategy pursued by the Belle II Collaboration at KEK.
Experimental prospects and implications
Future facilities increase sensitivity by extending collision energy, luminosity, and specialized detector coverage. The High-Luminosity LHC at CERN will improve limits on prompt diphoton resonances and enable dedicated forward detectors such as FASER to catch light, weakly coupled ALPs that travel long distances before decaying. Proposed machines such as the Future Circular Collider studies at CERN and linear collider concepts would expand mass reach and precision, allowing separation of photon versus gluon couplings through rate and kinematic measurements. Complementary ideas from Pierre Sikivie at University of Florida emphasize that collider discovery of an ALP would connect to cosmological roles for light bosons, potentially informing dark matter models or early-universe dynamics.
Understanding causes and consequences matters beyond particle physics: a confirmed ALP coupling to photons would reshape theoretical priorities and catalyze international coordination of detectors across CERN, KEK, and other institutions, affecting funding and scientific workforce distribution. Environmentally, experiments that require large facilities bring territorial and societal considerations related to land use and global collaboration ethos. Practical detection remains model-dependent, so a suite of strategies—precision resonance searches, displaced-vertex programs, and dedicated forward experiments—gives the best chance that future colliders will reveal the presence and specific couplings of axion-like particles.