Experiments are proposed which address the question of the existence of the "invisible" axion for the whole allowed range of the axion decay constant. These experiments exploit the coupling of the axion to the electromagnetic field, axion emission by the sum, and/or the cosmological abundance and presumed clustering of axions in the halo of our galaxy.

• Received 13 July 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.1415