Gravitational collapse in the postinflationary Universe

The Universe may pass through an effectively matter-dominated epoch between inflation and Big Bang Nucleosynthesis during which gravitationally bound structures can form on subhorizon scales. In particular, the inflaton field collapse into halos, forming "large scale" structure in very early universe. We combine N-body simulations with high-resolution zoom-in regions non-relativistic Schr\"odinger-Poisson equations are used to resolve detailed, wave-like of halos. Solitonic cores inside them, matching formation axion-like particles late-time denote these objects \textit{inflaton stars}, by analogy boson stars. Based a semi-analytic formalism we compute their overall mass distribution shows that some will reach overdensities $10^{15}$ if lasts for 20 $e$-folds. radii most massive stars shrink below Schwarzschild radius, suggesting they could primordial black holes prior thermalization.