Astronomical Searches for Nonbarionic Dark Matter

Astronomical methods of searching for light Goldstone bosons (axions and arions), which are candidates for dark matter, are briefly discussed. Three processes for the coupling between axions and photons are considered: (a) the decay of axions into two photons; (b) the conversion of photons into axions in the magnetic fields of stars and interstellar and intergalactic media; (c) the inverse transformation of axions generated inside the cores of stars. The intergalactic light of clusters of galaxies and the brightness of the night sky are good candidates for searches for an emission line arising from the radiative decay of axions. The results of observations made with the 6 m telescope of the Special Astrophysical Observatory do not provide any evidence for the existence of the hadronic axion decay line. The best upper limit for the photon-axion coupling constant is derived from linear polarization observations of magnetic Ap stars.