The axion mass from 5D small instantons

Tony Gherghetta, Valentin V. Khoze, Alex Pomarol, Yuri Shirman

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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.

Original languageEnglish (US)
Article number63
JournalJournal of High Energy Physics
Issue number3
StatePublished - Mar 1 2020

Bibliographical note

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This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited

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© 2020, The Author(s).


  • Field Theories in Higher Dimensions
  • Solitons Monopoles and Instantons


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