Axion-like particle oscillations

String theory compactifications may generate many light axion-like particles (ALPs) with weak couplings to electromagnetism. In general, a large number of ALPs exist, linear combination having potentially observable coupling The basis in which only one ALP couples electromagnetism is general misaligned the mass basis. This leads mixing between `electromagnetic' and `hidden' that do not interact directly photon. process analagous neutrino oscillations. I will discuss phenomenological consequences this for astrophysical signals, particular showing it significantly reduce predicted signal experiments such as CERN Axion Solar Telescope.