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arxiv 2105.01406 v2 pith:6ATTNTW7 submitted 2021-05-04 hep-ph astro-ph.HEhep-ex

Axion Dark Matter: What is it and Why Now?

classification hep-ph astro-ph.HEhep-ex
keywords axionmatterdarkparticlecandidatereviewastrophysicalaudience
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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The axion has emerged in recent years as a leading particle candidate to provide the mysterious dark matter in the cosmos, as we review here for a general scientific audience. We describe first the historical roots of the axion in the Standard Model of particle physics and the problem of charge-parity invariance of the strong nuclear force. We then discuss how the axion emerges as a dark matter candidate, and how it is produced in the early Universe. The symmetry properties of the axion dictate the form of its interactions with ordinary matter. Astrophysical considerations restrict the particle mass and interaction strengths to a limited range, which facilitates the planning of experiments to detect the axion. A companion review discusses the exciting prospect that the axion could {indeed} be detected in the near term in the laboratory.

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Cited by 10 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. A Near-Cutoff Waveguide Haloscope for sub-meV Dark Matter

    hep-ph 2026-05 unverdicted novelty 7.0

    A novel waveguide haloscope concept using near-cutoff slow-wave response for sub-meV bosonic dark matter, projecting dark photon sensitivity of ε≈2.1×10^{-15} at 0.1 meV.

  2. Any Light Particle Searches with ALPS II: first science results

    hep-ex 2025-12 unverdicted novelty 7.0

    ALPS II reports no detection of axion-like particles and establishes improved 95% CL upper limits on di-photon couplings of 1.5e-9 GeV^-1 for masses below 0.1 meV, plus limits for scalar, vector, and tensor bosons.

  3. Searching for axions with quantum interferometry

    hep-ph 2026-04 unverdicted novelty 6.0

    Axion-photon coupling imprints measurable Aharonov-Bohm and Berry phases in superconducting circuits and interferometers, projecting sensitivity to g_aγγ ~ 7.8e-14 GeV^{-1} at m_a ~ 1e-10 eV.

  4. Searching for axions with time resolved pulsar polarimetry

    hep-ph 2026-03 unverdicted novelty 6.0

    Time-resolved optical polarimetry of the Crab pulsar is used to place bounds on the axion-photon coupling via oscillating axion fields induced by the pulsar's magnetic field.

  5. Weakly supervised machine learning for model-agnostic searches of new phenomena in the $\gamma$-ray sky

    astro-ph.HE 2026-07 conditional novelty 5.0

    Weakly supervised classifiers trained on background-versus-mixture samples can identify anomalous gamma-ray sources without labeled signal templates, approaching supervised performance in controlled benchmarks.

  6. Axions Create Singularities on Extremal Horizons

    hep-th 2026-05 unverdicted novelty 5.0

    Axions cause singularities on the horizons of extremal rotating charged black holes for almost all axion mass and coupling values.

  7. Dimming of Photon Ring due to Photon-Axion Conversion around Kerr Black Holes

    gr-qc 2026-05 unverdicted novelty 5.0

    Photon-axion conversion near Kerr black holes produces dimming of photon spectral luminosity that increases with black hole spin, magnetic field strength, and photon-axion coupling, most efficiently at high frequencies.

  8. Prospects for probing neutral vector-like leptons via pair production at muon collider

    hep-ph 2026-06 unverdicted novelty 3.0

    Simulations indicate a 6 TeV muon collider with 4 ab^{-1} can reach >5σ significance for neutral doublet VLLs of 1.3-3 TeV mass using 4j2μ and 2ℓ2μ + missing energy channels under polarized beams.

  9. Tracing Ultra Light Axions in Post-reionization, Lyman-$\alpha$ and CMB Missions

    astro-ph.CO 2026-06 unverdicted novelty 3.0

    Fisher forecasts indicate joint post-reionization LSS cross-spectra and CMB-S4-like data can reach O(10^{-4}) uncertainty on ultra-light axion fraction for m_a ≲ 10^{-28} eV, with peak sensitivity near 10^{-25} eV.

  10. A search for heavy axion-like particles in light-by-light scattering at the FCC-hh

    hep-ph 2026-03 unverdicted novelty 3.0

    Computes production cross sections and sensitivity limits for heavy ALPs in light-by-light scattering at FCC-hh across pp, pPb, and PbPb modes.