Enhanced Preheating after Multi-Field Inflation: On the Importance of
  being Special
  We discuss preheating after multi-field inflation in the presence of several
preheat matter fields that become light in the vicinity of (but not at) the
inflatons' VEV, at distinct extra-species-points (ESP); this setup is motivated
by inflationary models that include particle production during inflation,
e.g.trapped inflation, grazing ESP encounters or modulated trapping, among
others. While de-phasing of inflatons tends to suppress parametric resonance,
we find two new effects leading to efficient preheating: particle production
during the first in-fall (efficient if many preheat matter fields are present)
and a subsequent (narrow) resonance phase (efficient if an ESP happens to be at
one of several distinct distances from the inflatons' VEV). Particles produced
during the first in-fall are comprised of many species with low occupation
number, while the latter are made up of a few species with high occupation
number.
  We provide analytic descriptions of both phases in the absence of
back-reaction, which we test numerically. We further perform lattice
simulations to investigate the effects of back-reaction. We find resonances to
be robust and the most likely cause of inflaton decay in multi-field trapped
inflation if ESP distributions are dense.
