We study gravitational creation of light fermions in the presence of
classical scalar metric perturbations about a flat Friedmann-Lemaitre-
Robertson-Walker (FLRW) background. These perturbations can be large during
preheating, breaking the conformal flatness of the background spacetime. We
compute numerically the total number of particles generated by the modes of the
metric perturbations which have grown sufficiently to become classical. In the
absence of inhomogeneities massless fermions are not gravitationally produced,
and then this effect may be relevant for abundance estimates of light
gravitational relics.Comment: 17 pages, 7 figures, accepted for publication in Nuclear Physics
