Preheating of fermions

In inflationary cosmology, the particles constituting the Universe are crea ted after inflation in the process of reheating due to their interaction wi th the oscillating inflaton field. In the bosonic sector, the leading chann el of particle production is the non-perturbative regime of parametric reso nance, preheating, during which bosons are created exponentially fast. Paul i blocking prohibits the unbounded creation of fermions. For this reason, i t has been silently assumed that the creation of fermions can be treated wi th perturbation theory for the decay of individual inflatons. We consider t he production of fermions interacting with the coherently oscillating infla tons. We find that the actual particle production occurs in a regime of the parametric excitation of fermions, leading to preheating of fermions. Ferm ion preheating differs significantly from the perturbative expectation. It turns out that the number density of fermions varies periodically with time . The total number of fermions quickly saturates to an average value within a broad range of momenta proportional to q(1/4), where q is the usual reso nance parameter. The resonant excitation of fermions may affect the transfe r of inflaton energy, estimations of the reheating temperature, and the abu ndance of superheavy fermions and gravitinos. Back in the bosonic sector, o utside of the parametric resonance bands there is an additional effect of p arametric excitation of bosons with bounded occupation number in the moment um range proportional to q(1/4). (C) 1999 Elsevier Science B.V. All rights reserved. PACS: 98.80.Cq.