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Axions and the Strong CP Problem

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arxiv 0807.3125 v2 pith:WN5WOE6M submitted 2008-07-20 hep-ph astro-phhep-exhep-th

classification hep-phastro-phhep-exhep-th
keywords axionproblemthetadatalesssimstrongangleastrophysical
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

Current upper bounds of the neutron electric dipole moment constrain the physically observable quantum chromodynamic (QCD) vacuum angle $|\bar\theta| \lesssim 10^{-11}$. Since QCD explains vast experimental data from the 100 MeV scale to the TeV scale, it is better to explain this smallness of $|\bar\theta|$ in the QCD framework, which is the strong \Ca\Pa problem. Now, there exist two plausible solutions to this problem, one of which leads to the existence of the very light axion. The axion decay constant window, $10^9\ {\gev}\lesssim F_a\lesssim 10^{12} \gev$ for a ${\cal O}(1)$ initial misalignment angle $\theta_1$, has been obtained by astrophysical and cosmological data. For $F_a\gtrsim 10^{12}$ GeV with $\theta_1<{\cal O}(1)$, axions may constitute a significant fraction of dark matter of the universe. The supersymmetrized axion solution of the strong \Ca\Pa problem introduces its superpartner the axino which might have affected the universe evolution significantly. Here, we review the very light axion (theory, supersymmetrization, and models) with the most recent particle, astrophysical and cosmological data, and present prospects for its discovery.

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Cited by 21 Pith papers

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

  1. On the Gravitational Origin of the QCD Axion

    hep-th 2025-06 accept novelty 7.0 of 10

    Derivative-coupled gravitational axions cannot solve the strong CP problem; Weyl-invariant Einstein-Cartan gravity is identified as the only promising framework for a gravitational QCD axion.

  2. Prominent enhancement of axion thermalization rate from axion-kaon interactions

    hep-ph 2025-05 conditional novelty 7.0 of 10

    Axion-kaon scattering, previously omitted from axion thermalization calculations, exceeds the axion-pion channel near T=130 MeV and tightens the Planck Delta N_eff bound on f_a by about 30%.

  3. Broadband Search for Axion Dark Matter via Shift Current

    hep-ph 2025-05 conditional novelty 7.0 of 10

    A proposed axion haloscope using shift-current difference frequency generation in the Weyl semimetal TaAs could probe QCD axions at 10-100 meV, assuming a 10^8 V/m, 100 ps THz drive field is achievable.

  4. Spinoptics in the presence of axion-like particles in curved spacetime

    gr-qc 2026-07 accept novelty 6.5 of 10

    Spinoptics equations for axion–Maxwell theory yield helicity-dependent photon trajectory corrections from both spacetime curvature and arbitrary axion profiles.

  5. Sign-Flipping Axion Potentials via Kapitza-Type Modulation by Heavy Axions

    hep-ph 2025-09 accept novelty 6.0 of 10

    Coherent oscillations of a heavy axion change the sign of a light axion's effective potential, trapping it in a false vacuum and boosting its dark matter abundance.

  6. Towards a Heterotic Axiverse

    hep-th 2025-09 conditional novelty 6.0 of 10

    Generic heterotic axions are heavier than in type IIB; the Strong CP problem is typically unsolved, and a light fuzzy dark matter axion requires a no-gaugino-condensation anisotropic fibred Calabi-Yau.

  7. Torsion induced current-scalaron coupling in Einstein-Cartan gravity

    hep-ph 2025-07 conditional novelty 6.0 of 10

    In Einstein-Cartan gravity, torsion-current couplings induce scalaron-current and scalaron Chern-Simons interactions, with explicit decay constants and a classification of their asymptotic behavior.

  8. Unified study of two-meson and axion-meson production from semileptonic tau decays within resonance chiral framework

    hep-ph 2025-07 conditional novelty 6.0 of 10

    Within a resonance chiral model, hadron resonances boost predicted tau decays into pion/K plus axion by factors of 7.5 and 19.2, with branching ratios and forward-backward asymmetries also predicted.

  9. First Constraint on Axion-Photon Coupling $g_{\gamma}$ from Neutron Star Observations

    hep-ph 2025-06 reject novelty 6.0 of 10

    The paper derives a first bound on the dimensionless axion-photon coupling gγ from pulsar polarization data, reporting |gγ|<0.93 at 1σ for axion masses below 10^-11 eV, via a neutron-star-induced axion field.

  10. All axion dark matter from supersymmetric models

    hep-ph 2025-02 conditional novelty 6.0 of 10

    For Z_4^R and Z_8^R discrete R-symmetries, R-parity violating couplings of order 10^-7 make the lightest supersymmetric particle decay in 10^-3 to 10 seconds, so the dark matter is entirely axion cold dark matter.

  11. Probing Light Particles With Optically Trapped Sensors Through Nucleon Scattering

    hep-ph 2025-01 conditional novelty 6.0 of 10

    Optically trapped nanosphere arrays could detect nuclear recoils from solar ALPs, sub-keV pseudoscalar/vector dark matter, and Earth-bound dark matter, opening new tabletop search windows in previously unconstrained p...

  12. Reappraisal of the Constraints on Heavy Axion-like Particles from Gamma-Ray Bursts

    hep-ph 2026-07 conditional novelty 5.0 of 10

    Realistic GRB parameters weaken previous ALP cooling bounds, but ALP-induced secondary fireballs in GRBs could still be probed via isotropic X-ray emission from future telescopes.

  13. ALP and $Z^\prime$ boson at the Electron-Ion collider

    hep-ph 2026-01 conditional novelty 5.0 of 10

    Projected EIC tri-electron searches would constrain electron-coupled ALPs and Z' bosons more strongly than current experiments at masses of about 10-100 GeV and 10-30 GeV, respectively.

  14. New axion contribution to the two-photon decays of neutral pions

    hep-ph 2025-02 conditional novelty 5.0 of 10

    Axion-pion mixing adds a new next-to-leading-order term to the pi0 to gamma gamma decay width that is negligible for standard light axions but may matter for MeV-scale heavy axions.

  15. Serendipitous supersymmetric solution to the strong CP problem

    hep-ph 2026-07 conditional novelty 4.5 of 10

    Anomaly-free discrete R-symmetries plus Kim-Nilles regeneration of the mu term force an accidental U(1)_PQ whose spontaneous breaking yields a SUSY DFSZ axion that solves strong CP.

  16. A multi-axion model of inflation and dark matter

    hep-ph 2026-07 reject novelty 4.0 of 10

    A 300-mode Kaluza-Klein axion tower is proposed as a unified inflaton and dark-matter sector, but the lightest state's quoted lifetime contradicts the paper's own decay-rate formula.

  17. Flavor in Ninths and a Discrete Gauge Origin of the QCD Axion

    hep-ph 2026-03 reject novelty 4.0 of 10

    A 'flavor in ninths' fit is claimed to force a Z18 discrete gauge symmetry whose flavon doubles as the QCD axion, fixing the axion mass at 7-12 μeV with DFSZ-II coupling.

  18. Dark Matter and CP Violation in Some Symmetry-Constrained 3HDMs

    hep-ph 2025-06 conditional novelty 4.0 of 10

    S3-symmetric three-Higgs-doublet models allow dark matter in a 29-42 GeV window, exclude heavy candidates above 500 GeV, and admit MeV-scale light scalars, while continuous-symmetry variants produce mass-degenerate da...

  19. Cosmological constraints on small-scale primordial non-Gaussianity

    astro-ph.CO 2025-05 conditional novelty 4.0 of 10

    Current pulsar-timing, CMB, BAO and PBH data constrain the small-scale local f_NL to -10.0 < f_NL < 1.2 for a monochromatic primordial power spectrum, with that constraint conditional on the spectral amplitude A_zeta = 10^-2.

  20. Multiple-cavities interferometric analysis for dark matter axions directional-sensitive search based on signal cross-correlation processing

    hep-ex 2025-02 conditional novelty 4.0 of 10

    Cross-correlating signals from multiple haloscope cavities gives a modest SNR growth advantage over power summation and yields a daily modulation in the cross-correlation imaginary part that could characterize axion v...

  21. QCD CP-violation scenario for a revised cosmological dynamics: analysis of the binned Pantheon Sample of Super Novae Ia

    astro-ph.CO 2026-07 reject novelty 3.0 of 10

    The paper fits a dark-matter–dark-energy interaction model from a complex scalar field to binned Pantheon SNeIa data and claims to explain the redshift-running H0, but the derivation's equations are internally inconsistent.

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