Supermassive Primordial Black Holes From Inflation

TL;DR

This paper investigates the potential formation of supermassive primordial black holes from inflation-induced density perturbations, emphasizing the need for highly non-Gaussian fluctuations to evade observational constraints.

Contribution

It proposes a model of multi-field inflation capable of generating the necessary non-Gaussianity for SMBH formation from primordial perturbations.

Findings

Highly non-Gaussian perturbations can evade CMB constraints.

A non-minimal, self-interacting curvaton model can produce such non-Gaussianities.

Highlights challenges and features needed for models to form SMBHs from primordial fluctuations.

Abstract

There is controversy surrounding the origin and evolution of our universe's largest supermassive black holes (SMBHs). In this study, we consider the possibility that some of these black holes formed from the direct collapse of primordial density perturbations. Since the mass of a primordial black hole is limited by the size of the cosmological horizon at the time of collapse, these SMBHs must form rather late, and are naively in conflict with constraints from CMB spectral distortions. These limits can be avoided, however, if the distribution of primordial curvature perturbations is highly non-Gaussian. After quantifying the departure from Gaussianity needed to evade these bounds, we explore a model of multi-field inflation -- a non-minimal, self-interacting curvaton model -- which has all the necessary ingredients to yield such dramatic non-Gaussianities. We leave the detailed model building and numerics to a future study, however, as our goal is to highlight the challenges associated with forming SMBHs from direct collapse and to identify features that a successful model would need to have. This study is particularly timely in light of recent observations of high-redshift massive galaxy candidates by the James Webb Space Telescope as well as evidence from the NANOGrav experiment for a stochastic gravitational wave background consistent with SMBH mergers.