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The QCD axion's coupling to photons is often assumed to lie in a narrow bandas a function of the axion mass. We demonstrate that several simple mechanisms,in addition to the photophilic clockwork axion already in the literature, cansignificantly extend the allowed range of couplings. Some mechanisms we presentgeneralize the KNP alignment scenario, widely studied as a model of inflation,to the phenomenology of a QCD axion. In particular we present KSVZ-likerealizations of two-axion KNP alignment and of the clockwork mechanism. Such a"confinement tower" realization of clockwork may prove useful in a variety ofmodel-building contexts. We also show that kinetic mixing of the QCD axion witha lighter axion-like particle can dramatically alter the QCD axion's couplingto photons, differing from the other models we present by allowingnon-quantized couplings. The simple models that we present fully cover therange of axion-photon couplings that could be probed by experiments. Theymotivate growing axion detection efforts over a wide space of masses andcouplings.

Experimental Targets for Photon Couplings of the QCD Axion