Gravitational Collapse in the Post-Inflationary Universe

TL;DR

This paper explores how gravitational collapse of the inflaton field during a post-inflationary matter-dominated epoch can lead to early universe structures, including potential primordial black holes, using simulations and semi-analytic models.

Contribution

It introduces a novel combination of N-body and Schrödinger-Poisson simulations to study inflaton halo formation and predicts the possible formation of primordial black holes from inflaton star collapse.

Findings

Inflaton halos can reach overdensities of 10^15 within 20 e-folds.

Inflaton stars can have radii smaller than the Schwarzschild radius.

Some inflaton stars may collapse into primordial black holes.

Abstract

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