Can massive primordial black holes be produced in mild waterfall hybrid inflation?

TL;DR

This paper investigates whether massive primordial black holes can form during hybrid inflation, using a combined stochastic and delta N formalism to perform non-perturbative calculations, revealing overproduction of PBHs under certain conditions.

Contribution

It provides a quantitative, non-perturbative analysis of PBH formation in hybrid inflation without assuming specific inflation models.

Findings

PBHs tend to be overproduced when the waterfall phase is prolonged.

The PBH mass scale can become sizable with extended waterfall phase.

The study offers a new numerical approach combining stochastic and delta N formalisms.

Abstract

We studied the possibility whether the massive primordial black holes (PBHs) surviving today can be produced in hybrid inflation. Though it is of great interest since such PBHs can be the candidate for dark matter or seeds of the supermassive black holes in galaxies, there have not been quantitatively complete works yet because of the non-perturbative behavior around the critical point of hybrid inflation. Therefore, combining the stochastic and $\delta N$ formalism, we numerically calculated the curvature perturbations in a non-perturbative way and found, without any specific assumption of the types of hybrid inflation, PBHs are rather overproduced when the waterfall phase of hybrid inflation continues so long that the PBH scale is well enlarged and the corresponding PBH mass becomes sizable enough.