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Recent Progress in the Physics of Axions and Axion-Like Particles

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arxiv 2012.05029 v3 pith:ZEN4L7RR submitted 2020-12-09 hep-ph hep-th

Recent Progress in the Physics of Axions and Axion-Like Particles

classification hep-ph hep-th
keywords axionaxionscouplingsphysicsprogressrecentaxion-likefield
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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The axion is a light pseudoscalar particle postulated to solve issues with the Standard Model, including the strong CP problem and the origin of dark matter. In recent years, there has been remarkable progress in the physics of axions in several directions. An unusual type of axion-like particle termed the relaxion was proposed as a new solution to the weak scale hierarchy problem. There are also new ideas for laboratory, astrophysical, or cosmological searches for axions; such searches can probe a wide range of model parameters that were previously inaccessible. On the formal theory side, the weak gravity conjecture indicates a tension between quantum gravity and a trans-Planckian axion field excursion. Many of these developments involve axions with hierarchical couplings. In this article, we review recent progress in axion physics, with particular attention paid to hierarchies between axion couplings. We emphasize that the parameter regions of hierarchical axion couplings are the most accessible experimentally. Moreover, such regions are often where important theoretical questions in the field are addressed, and they can result from simple model-building mechanisms.

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Cited by 14 Pith papers

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

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    A dc SQUID operated at the flux sweet spot with lock-in modulation yields an ultra-broadband axion search with projected sensitivity |g_aγγ| ≳ 10^{-16} GeV^{-1} across 15 orders of magnitude in mass.

  2. The $B^+ \to K^+ \nu \bar \nu$ decay as a search for the QCD axion

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    Model-independent reinterpretation of Belle II B+ → K+ νν̄ data using public kinematic mapping yields a factor-of-nine improvement on the limit for B+ → K+ a and constrains the axion's b-s flavor-changing coupling.

  3. Chiral Gravitational Wave Background from Audible Axion via Nieh-Yan Term

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  4. The structure of multi-axion solutions to the strong CP problem

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    Multi-axion solutions to the strong CP problem produce varied mass-coupling patterns set by PQ symmetry breaking structure and QCD-EM anomaly alignment, summarized by a general sum rule for N-axion systems.

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    hep-ph 2026-05 unverdicted novelty 6.0

    Multi-axion theories solving the strong CP problem produce varied mass-coupling relations via a general sum rule that depends on the details of PQ symmetry breaking and anomaly alignments.

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    hep-th 2026-06 unverdicted novelty 5.0

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    QCD axions constrain F-theory base threefolds to have rigid or flux-rigidified divisors, yielding typical axion masses around 10^{-9} eV and decay constants near 10^{15} GeV in allowed regions.

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    hep-th 2026-05 unverdicted novelty 5.0

    F-theory models with the Standard Model spectrum are constrained by QCD axion physics, yielding typical detectable axion masses around 10^{-9} eV and decay constants around 10^{15} GeV in allowed regions.

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