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Wednesday, November 15, 2023 at 2:00pm
Physical Sciences Building, 401
245 East Avenue
Axion couplings in Grand Unified Theories
The couplings of axions to gauge bosons are highly restricted in Grand Unified Theories. The topological nature of these couplings allows them to be matched from the UV to the IR, and the ratio of the anomaly with photons and gluons for any axion is fixed by unification. This implies that there is a single axion, the QCD axion, with an anomalous coupling to photons. Other light axion-like particles can couple to photons by mixing through the QCD axion portal and lie to the right of the QCD line in the mass-coupling plane. Axions which break the unification relation between gluon and photon couplings are necessarily charged under the GUT gauge group and become heavy from perturbative mass contributions. In higher dimensions, symmetry breaking by boundary conditions can similarly break the GUT relations between couplings but also lead to a large axion mass. A discovery of an axion to the left of the QCD line can rule out simple Grand Unified models. Axion searches are therefore tabletop and astrophysical probes of Grand Unification.