Time-Scales for Nonlinear Processes in Preheating after Multifield
  Inflation with Nonminimal Couplings
  We have conducted extensive lattice simulations to study the post-inflation
dynamics of multifield models involving nonminimal couplings. We explore the
parameter dependence of preheating in these models and describe the various
time-scales that control such nonlinear processes as energy transfer,
re-scattering, and the approach to radiation-domination and thermalization. In
the limit of large nonminimal couplings ($\xi_I \sim 100$), we find that
efficient transfer of energy from the inflaton condensate to radiative degrees
of freedom, emergence of a radiation-dominated equation of state, and the onset
of thermalization each consistently occur within $N_{\rm reh} \lesssim 3$
$e$-folds after the end of inflation, largely independent of the values of the
other couplings in the models. The exception is the case of negative
ellipticity, in which there is a misalignment between the dominant direction in
field-space along which the system evolves and the larger of the nonminimal
couplings $\xi_I$. In those cases, the field-space-driven parametric resonance
is effectively shut off. More generally, the competition between the scalar
fields' potential and the field-space manifold structure can yield interesting
phenomena such as two-stage resonances. Despite the explosive particle
production, which can lead to a quick depletion of the background energy
density, the nonlinear processes do not induce any super-horizon correlations
after the end of inflation in these models, which keeps predictions for CMB
observables unaffected by the late-time amplification of isocurvature
fluctuations. Hence the excellent agreement between primordial observables and
recent observations is preserved for this class of models, even when we
consider post-inflation dynamics.
