Freeze-in from Preheating
  We consider the production of dark matter during the process of reheating
after inflation. The relic density of dark matter from freeze-in depends on
both the energy density and energy distribution of the inflaton scattering or
decay products composing the radiation bath. We compare the perturbative and
non-perturbative calculations of the energy density in radiation. We also
consider the (likely) possibility that the final state scalar products are
unstable. Assuming either thermal or non-thermal energy distribution functions,
we compare the resulting relic density based on these different approaches. We
show that the present-day cold dark matter density can be obtained through
freeze-in from preheating for a large range of dark matter masses.
