Axion mass prediction from minimal grand unification

We propose a minimal realization of the Peccei-Quinn mechanism in a realistic SU(5) model, where the axion mass is directly connected to the grand unification scale. Accounting for constraints from proton decay, collider searches and gauge coupling unification, we predict the axion mass ma [4.8,6.6] neV. The upper bound relaxes to ma<330 neV for a tuned flavor structure of the proton decay operators. The predicted mass window will be complementarily probed by the axion dark matter experiments ABRACADABRA and CASPER-Electric, which could provide indirect evidence for the scale of grand unification before the observation of proton decay.