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

Automated summary

String theory compactifications may produce numerous light axion-like particles with weak electromagnetic couplings. A linear combination of these particles may have an observable coupling to electromagnetism. However, the basis in which one particle couples to electromagnetism is usually misaligned with the mass basis, resulting in mixing with other hidden particles that do not directly interact with photons. This mixing can substantially reduce the predicted signal in experiments such as the CERN Axion Solar Telescope.