Primordial Black Holes as All Dark Matter

TL;DR

The paper argues that primordial black holes can constitute all dark matter within a minimal framework. It introduces a smooth-hybrid new double-inflation model in which preheating after the first inflation generates a sharply peaked PBH mass function spanning $10^{-8}$ to $10^{5}\,M_\odot$, with PBH mass tied to the running of the scalar spectral index. It analyzes observational constraints, showing narrow mass peaks can evade limits and make falsifiable predictions for Planck-scale observations. It also discusses detection avenues via microlensing, CMB effects, gravitational waves, and entropy-based motivation for PBHs as DM.

Abstract

We argue that a primordial black hole is a natural and unique candidate for all dark matter. We show that, in a smooth-hybrid new double inflation model, a right amount of the primordial black holes, with a sharply-defined mass, can be produced at the end of the smooth-hybrid regime, through preheating. We first consider masses < 10^(-7)M_sun which are allowed by all the previous constraints. We next discuss much heavier mass 10^5 M_sun hinted at by entropy, and galactic size evolution, arguments. Effects on the running of the scalar spectral index are computed.

Figures (2)

• Figure 1: Power spectrum of the curvature perturbation. We take $\mu= 4 v = 7.14\times 10^{-4}$, $M=0.29$, $c=0.1$ and $g= 2\times 10^{-5}$.
• Figure 2: $n_s$ and $dn_s/d\ln k$ for PBH mass $M_{\rm BH}=10^5 M_\odot, 10^{-7}M_{\odot},$ and $10^{-8}M_{\odot}$.