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The Axion Mass from 5D Small Instantons

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arxiv 2001.05610 v1 pith:X3EUSLBN submitted 2020-01-16 hep-ph hep-th

classification hep-phhep-th
keywords axionmassinstantonscontributioninstantonsmallsolutionaction
verification ladder T0 review T1 audit T2 compute T3 formal
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We calculate a new contribution to the axion mass that arises from gluons propagating in a 5th dimension at high energies. By uplifting the 4D instanton solution to five dimensions, the positive frequency modes of the Kaluza-Klein states generate a power-law term in the effective action that inversely grows with the instanton size. This causes 5D small instantons to enhance the axion mass in a way that does not spoil the axion solution to the strong CP problem. Moreover this enhancement can be much larger than the usual QCD contribution from large instantons, although it requires the 5D gauge theory to be near the non-perturbative limit. Thus our result suggests that the mass range of axions (or axion-like particles), which is important for ongoing experimental searches, can depend sensitively on the UV modification of QCD.

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Cited by 3 Pith papers

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

  1. Suppressing Extra-Dimensional Axion Isocurvature Dynamically

    hep-ph 2026-07 conditional novelty 6.0 of 10

    Radion dynamics in warped 5D models enhance the axion decay constant during inflation, satisfying CMB isocurvature bounds at higher Hubble scales while restoring the QCD window afterward.

  2. The Minimal High-Quality QCD Axion

    hep-ph 2026-07 conditional novelty 5.5 of 10

    A flat-interval 5D U(1) Wilson-line axion with 4D KSVZ/DFSZ anomaly sector supplies exponential quality protection while remaining minimal.

  3. 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.

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