Year: 2026
Type: article
Abstract: A bstract We consider the coupling of axions to gauge bosons in higher-dimensional Grand Unified Theories (GUT) inspired by string theory constructions with D-branes on orbifold singularities, the so-called orbifold GUTs. Due to their topological properties, axion couplings to gauge bosons are independent of the gauge symmetry reduction mechanism and the background geometry — they only depend on the embedding of the SM into the UV gauge group. There are two kinds of axions in this class of theories: axions coming from gauge fields in the bulk and axions localised on the boundaries. The axion-photon coupling for the bulk axions coincide with the results from 4-dimensional GUTs, where axions which couple to photons necessarily couple also to QCD. The brane-localised axions can couple to photons independently of the QCD coupling, but if gauge couplings are approximately unified, they have a much more severe quality problem. We show that in generic UV completions they are expected to get large masses from instantons on the boundaries. This means that the ratio g aγγ / m a is below (or equal to) the QCD axion value for all axions in orbifold GUTs, as is the case for unified theories in 4d.
Source: Journal of High Energy Physics
Authors: Prateek Agrawal, Michael Nee, Mario Reig
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7108224419
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