Oscillon formation during inflationary preheating with general relativity

We study the nonperturbative evolution of inflationary fluctuations during preheating using fully nonlinear general-relativistic field-theory simulations. We choose a single-field inflationary model that is consistent with observational constraints and start the simulations at the end of inflation with fluctuations both in the field and its conjugate momentum. Gravity enhances the growth of density perturbations, which then collapse and virialize, forming long-lived stable oscillon-like stars that reach compactnesses C/R10^-3--10^-2. We find that C increases for larger field models, until it peaks due to the interplay between the overdensity growth and Hubble expansion rates. While gravitational effects can play an important role in the formation of compact oscillons during preheating, the objects are unlikely to collapse into primordial black holes without an additional enhancement of the initial inflationary fluctuations.