López Maroto, Antonio2023-06-202023-06-201999-02-020556-282110.1103/PhysRevD.59.063501https://hdl.handle.net/20.500.14352/59336© 1999 The American Physical Society. I thank Ed. Copeland and A. Dobado for useful suggestions. This work has been partially supported by the Ministerio de Educación y Ciencia (Spain) (CICYT AEN96-1634). The author also acknowledges support from SEUID-Royal Society.We study the production of massive fermions in arbitrary vector and axial-vector classical backgrounds using effective action techniques. A perturbative calculation shows the different features of each field and in particular it is seen that pure temporal axial fields can produce particles whereas it is not possible for a pure vector background. We also analyze from a non-perturbative point of view a particular configuration with constant electric and axial fields and show that the presence of the axial background inhibits the production from the electric field. [S0556-2821(99)04504-X].engjournal articlehttp://dx.doi.org/10.1103/PhysRevD.59.063501http://journals.aps.org/open access53String cosmologyInflationUniverseTorsionVacuumModelTimeFísica (Física)22 Física