NEUTRINO DECAY OF A PSEUDOSCALAR PARTICLE IN A MAGNETIC-FIELD

By considering the axion as an example, the field-induced decay of a p seudoscalar particle into a neutrino-antineutrino pair, a --> nu<(nu)o ver bar>, is studied for the case of a constant external magnetic fiel d. The crossing channel-the axionic decay of a massive neutrino, nu(i) --> nu(j)a - is investigated under analogous conditions. A general ex pression for the vertex of effective a nu(i)nu(j) interaction has been obtained in the second order of perturbation theory. The expressions for the decay amplitudes and probabilities reveal a catalyzing role of an external field.