Astronomical searches for axions: observations at the SAO 6-m telescope

The astronomical methods of searching for light Goldstone bosons are discussed. The basic idea is to use processes of coupling between Goldstone bosons and photons, including (i) the decay of axions into two photons, and (ii) the transformation of photons into massless axions in the magnetic fields of stars and intergalactic media. The intergalactic light of clusters of galaxies and the brightness of the night sky owing to axions in the halo of our Galaxy are good candidates in which to search for an emission line arising from the radiative decay of axions. The results of observations made by the SAO 6-m telescope in Russia do not provide any evidence for the existence of the hadronic axion decay line. The best upper limit on the photon-arion coupling constant is given by linear polarimetric observations of magnetic Ap stars.