Gravitational Fermion Production in Inflationary Cosmology
  We revisit the gravitational production of massive Dirac fermions in
inflationary cosmology with a focus on clarifying the analytic computation of
the particle number density in both the large and the small mass regimes. For
the case in which the masses of the gravitationally produced fermions are small
compared to the Hubble expansion rate at the end of inflation, we obtain a
universal result for the number density that is nearly independent of the
details of the inflationary model. The result is identical to the case of
conformally coupled scalars up to an overall multiplicative factor of order
unity for reasons other than just counting the fermionic degrees of freedom.
