  We study the post-inflation dynamics of multifield models involving
nonminimal couplings using lattice simulations to capture significant nonlinear
effects like backreaction and rescattering. We measure the effective equation
of state and typical time-scales for the onset of thermalization, which could
affect the usual mapping between predictions for primordial perturbation
spectra and measurements of anisotropies in the cosmic microwave background
radiation. For large values of the nonminimal coupling constants, we find
efficient particle production that gives rise to nearly instantaneous
preheating. Moreover, the strong single-field attractor behavior that was
previously identified persists until the end of preheating, thereby suppressing
typical signatures of multifield models. We therefore find that predictions for
primordial observables in this class of models retain a close match to the
latest observations.

High Energy Physics - Phenomenology;Cosmology and Nongalactic Astrophysics;High Energy Physics - Theory