EFFECT OF A MAGNETIC-FIELD ON THE AXION LIFETIME

The axion decay a --> f (f) over tilde. induced by a constant external magnetic field is studied as an example of pseudoscalar-particle deca y into two charged fermions that is forbidden in a vacuum. The contrib utions of the first and higher Landau levels to the probability of the process are investigated. The results reveal the catalyzing effect of a magnetic field. That the axion lifetime is significantly reduced in a strong magnetic field can be of interest in astrophysical and cosmo logical applications-for example, this phenomenon can be used to refin e the lower limit on the axion mass if there were strong magnetic fiel ds in the early Universe. One-loop expressions for the a --> f (f) ove r tilde --> a transition amplitude are obtained in the presence of mag netic and crossed fields.