Probing the axion-photon coupling: phenomenological and experimental
  perspectives. A snowmass white paper
  We present a brief overview of the ongoing searches for the axion particle
via its coupling to photons. Both the classical QCD axions and more recently
proposed Axion-Like-Particles are considered. Astrophysical bounds on the
axion-photon coupling come from considerations of stellar energy loss during
Helium burning, in both low- and high-mass stars. Helioscopes look for
back-conversion of solar axions into x-ray photons in strong laboratory
magnetic fields. Finally, haloscopes aim to detect dark matter axions in our
galactic halo. Both types of searches are expecting significant advances in the
future, which will enable them to probe large, well-motivated parts of the
parameter space below the stellar cooling bounds.
