Formation of MACHO-Primordial Black Holes in Inflationary Cosmology

TL;DR

The paper addresses the challenge of explaining MACHOs as primordial black holes by introducing a multi-field inflationary scenario that generates a peaked isocurvature fluctuation spectrum. By coupling three scalar fields, with the inflaton driving inflation and a light isocurvature field whose amplitude is modulated to create a horizon-scale peak, the authors obtain a significant PBH formation probability at a chosen mass scale, exemplified around $0.1\,M_{\odot}$ with $\Omega_{\rm BH}\sim 10^{-3}$. They analyze the background evolution, fluctuation generation, and post-inflationary dynamics, deriving parameter constraints and providing a concrete set that yields the desired PBH mass spectrum. The work shows that PBHs compatible with MACHOs can arise without introducing breaks in the potential, and the framework can be extended to other PBH masses by adjusting a few parameters, offering a viable inflationary mechanism for nonbaryonic compact dark matter constituents.

Abstract

As a nonbaryonic explanation of massive compact halo objects, a phenomenological model is presented which predicts formation of primordial black holes at a desired mass scale. The required feature of initial density fluctuation is realized making use of the primordially isocurvature fluctuation generated in an inflationary universe model with multiple scalar fields.