Key points are not available for this paper at this time.
Axionlike particle (ALP) --photon couplings are modeled in large ensembles of string vacua and random matrix theories. In all cases, the effective coupling increases polynomially in the number of ALPs, of which hundreds or thousands are expected in the string ensembles, many of which are ultralight. The expected value of the couplings g₀10^-12 GeV^-1-10^-10 GeV^-1 provide viable targets for future x-ray telescopes and axion helioscopes, and in some cases are already in tension with existing data.
Halverson et al. (Thu,) studied this question.