Resonant production of fermions in an axial background

We consider the resonant production of fermions from an oscillating axialbackground. The classical evolution of the axial field is given by that of amassive pseudovector field, as suggested by the renormalizability of thetheory. We look upon both the massive and the massless fermion production froma perturbative point of view. We obtain the corresponding spectrum and angulardistributions for the different spins or helicities in the particular case of aspatial-like axial field. We also extend our study to the non-perturbativeregime in the massless case and compare the results with the perturbative ones.Comment: 16 pages, LaTeX, 12 figures; new comments and references added, version to appear in Phys. Rev.