Axion-photon couplings in invisible axion models.

We reexamine the axion-photon couplings in various invisible axion models motivated by the recent proposal of using optical interferometry at the ASST facility at the SSCL to search for the axion. We illustrate that the assignment of U(1){sub PQ} charges for the fermion fields plays an important role in determining the couplings. Several simple nonminimal invisible axion models with suppressed and enhanced axion-photon couplings are constructed, respectively. We also discuss the implications of possible new experiments to detect solar axions by conversion to x rays in a static magnetic apparatus tracking the Sun.