Stochastic dynamics of multi-waterfall hybrid inflation and formation of primordial black holes

TL;DR

This paper demonstrates that multi-waterfall hybrid inflation models can produce astrophysical primordial black holes and observable gravitational waves, overcoming previous limitations of single-waterfall models through stochastic dynamics analysis.

Contribution

The study introduces an advanced stochastic algorithm for multi-waterfall hybrid inflation, showing it can generate astrophysical PBHs without fine-tuning, unlike single-waterfall models.

Findings

Primordial black holes of mass ~10^{20} g can form in multi-waterfall hybrid inflation.

Multiple waterfall fields (around 5) enable PBH formation with instantaneous reheating.

Observable gravitational waves are produced from curvature perturbations and defect dynamics.

Abstract

We show that a hybrid inflation model with multiple waterfall fields can result in the formation of primordial black hole (PBH) with an astrophysical size, by using an advanced algorithm to follow the stochastic dynamics of the waterfall fields. This is in contrast to the case with a single waterfall field, where the wavelength of density perturbations is usually too short to form PBHs of the astrophysical scale (or otherwise PBH are overproduced and the model is ruled out) unless the inflaton potential is tuned. In particular, we demonstrate that PBHs with masses of order $10^{20}\, {\rm g}$ can form after hybrid inflation consistently with other cosmological observations if the number of waterfall fields is about 5 for the case of instantaneous reheating. Observable gravitational waves are produced from the second-order effect of large curvature perturbations as well as from the dynamics of texture or global defects that form after the waterfall phase transition.