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| Axion models | |
|---|---|
| Name | Axion models |
| Caption | Conceptual diagram of axion parameter space and experimental searches |
| Field | Particle physics |
| Introduced | 1977 |
| Notable figures | Roberto Peccei, Helen Quinn, Frank Wilczek, Steven Weinberg, Wilczek, John Preskill, Mark Wise, Michael Dine, Anselm Zhitnitsky, Kim (Jihn E. Kim), Georg Raffelt, Pierre Sikivie |
| Key publications | Physical Review Letters, Physical Review D, Nuclear Physics B |
Axion models provide theoretical frameworks proposing a light pseudoscalar particle, the axion, originally introduced to resolve the strong CP problem in Quantum Chromodynamics and later considered as a dark matter candidate. These models connect high-energy symmetry breaking to low-energy phenomenology, guide experimental searches across collider, astrophysical, and laboratory contexts, and motivate cosmological implications from inflation to structure formation. Development spans analytic model-building, computational simulations, and collaborations among institutions and experiments.
Axion models originated with the Peccei–Quinn mechanism introduced by Roberto Peccei and Helen Quinn to explain the absence of CP violation in Quantum Chromodynamics; subsequent theoretical work by Steven Weinberg and Frank Wilczek identified the axion as the pseudo-Nambu–Goldstone boson. Model-building diversified through contributions from Jihn E. Kim, Anselm Zhitnitsky, John Preskill, Mark Wise, and Michael Dine, yielding benchmark frameworks used by experimental collaborations such as ADMX, CAST, CERN, and SNOLAB. Interdisciplinary connections link axion models to concepts studied at Fermilab, SLAC National Accelerator Laboratory, and by consortia like the Particle Data Group.
Axion models rest on spontaneously broken global symmetries and anomalies studied within Quantum Chromodynamics and effective field theory. The Peccei–Quinn symmetry U(1)_PQ is a global symmetry whose breaking yields a Nambu–Goldstone boson; instanton effects computed using techniques from Gerard 't Hooft and Alexander Polyakov generate a potential giving the axion a small mass. Chiral Lagrangians applied by Steven Weinberg and topological susceptibility calculations from lattice studies at CERN and Fermilab determine low-energy couplings to photons and fermions. Anomaly matching conditions and renormalization group flow analyzed by groups at Institute for Advanced Study and Perimeter Institute inform ultraviolet completions, while connections to grand unified theories explored at Harvard University and Princeton University affect model parameters.
Well-known classes include the KSVZ and DFSZ constructions developed respectively by Jihn E. Kim and Anselm Zhitnitsky (KSVZ), and by Michael Dine, Willy Fischler, and Mark Srednicki (DFSZ). KSVZ models introduce heavy quarks charged under U(1)_PQ; DFSZ models couple axions to two Higgs doublets in frameworks considered at Stanford University and Massachusetts Institute of Technology. Variants incorporate string-theoretic axions arising in compactifications studied at Institute for Advanced Study and Caltech, or "axion-like particles" discussed in the context of James Webb Space Telescope astrophysical probes and analyses by HEP collaborations. Other constructs include the "invisible axion" scenarios endorsed by John Preskill and the "clockwork" and "alignment" mechanisms analyzed by David Kaplan and Nima Arkani-Hamed-adjacent groups at MIT and Institute for Advanced Study.
Axion phenomenology spans astrophysical processes in Supernova 1987A, stellar cooling constraints from studies at Max Planck Institute for Astrophysics and University of Cambridge, and implications for cosmic microwave background measurements by Planck Collaboration and WMAP. In cosmology, axion dark matter production mechanisms include vacuum misalignment, string and domain wall decay simulations performed by teams at Lawrence Berkeley National Laboratory and Perimeter Institute, and production during reheating scenarios investigated at CERN Theory Division. Axion interactions with photons impact observations by H.E.S.S., Fermi Gamma-ray Space Telescope, and optical polarization studies by collaborations affiliated with European Southern Observatory. Laboratory manifestations influence precision tests at LIGO Laboratory and searches for oscillating electric dipole moments led by groups at Yale University and University of Washington.
Experimental programs include microwave cavity experiments like ADMX and HAYSTAC; helioscope projects such as CAST and planned IAXO; light-shining-through-wall experiments by collaborations connected to CERN and DESY; and birefringence and polarization campaigns at PVLAS. Collider probes are pursued at Large Hadron Collider experiments ATLAS and CMS as well as intensity facilities like Fermilab's Muon g-2 and Belle II at KEK. Astrophysical limits derive from observations of Supernova 1987A, red giant branch stars analyzed by Hubble Space Telescope teams, and helioseismology studies. Cosmological bounds use data from Planck Collaboration and large-scale surveys such as Sloan Digital Sky Survey.
Extensions link axion models to supersymmetry studied at CERN Theory Division and SLAC, grand unified theories considered at University of Chicago, and string compactifications analyzed by Max Planck Institute for Physics. Mechanisms like Kim–Nilles, alignment, clockwork, and rejuvenated heavy-axion frameworks connect to research groups at Institute for Advanced Study, Princeton University, and Harvard University. Embedding axions in inflationary scenarios involves collaborations associated with Harvard-Smithsonian Center for Astrophysics and Perimeter Institute, while coupling to hidden sectors is pursued in projects at Lawrence Berkeley National Laboratory and Fermilab.
Outstanding issues include precise determination of axion couplings from nonperturbative Quantum Chromodynamics calculations by lattice collaborations at CERN and Brookhaven National Laboratory, clarifying the role of topological defects in axion dark matter from simulations at Perimeter Institute, and designing sensitive detectors developed by ADMX and future consortia like IAXO. Cross-disciplinary opportunities link axion searches to gravitational-wave observatories such as LIGO and to astrophysical surveys conducted by LSST and James Webb Space Telescope. Progress will depend on coordinated efforts among universities, national laboratories, and international collaborations including CERN, Fermilab, DESY, and agencies funding fundamental physics.