Limits on primordial black holes detectability with Isatis: A BlackHawk tool

TL;DR

This paper critically reexamines the constraints on primordial black holes as dark matter candidates using the Isatis tool, revealing that assumptions significantly affect the limits and that only a narrow mass range can be constrained by Hawking radiation.

Contribution

The paper introduces the Isatis tool for analyzing Hawking radiation constraints and systematically assesses how assumptions impact PBH abundance limits.

Findings

Constraints vary by orders of magnitude based on assumptions.

Only PBHs with mass below ~10^{20} g can be constrained by Hawking radiation.

Upper mass window remains unconstrained by Hawking radiation.

Abstract

Primordial black holes (PBHs) are convenient candidates to explain the elusive dark matter (DM). However, years of constraints from various astronomical observations have constrained their abundance over a wide range of masses, leaving only a narrow window open at $10^{17}\,{\rm g} \lesssim M \lesssim 10^{22}\,$g for all DM in the form of PBHs. We reexamine this disputed window with a critical eye, interrogating the general hypotheses underlying the direct photon constraints. We review 4 levels of assumptions: i) instrument characteristics, ii) prediction of the (extra)galactic photon flux, iii) statistical method of signal-to-data comparison and iv) computation of the Hawking radiation rate. Thanks to Isatis, a new tool designed for the public Hawking radiation code BlackHawk, we first revisit the existing and prospective constraints on the PBH abundance and investigate the impact of assumptions i)-iv). We show that the constraints can vary by several orders of magnitude, advocating the necessity of a reduction of the theoretical sources of uncertainties. Second, we consider an "ideal" instrument and we demonstrate that the PBH DM scenario can only be constrained by the direct photon Hawking radiation phenomenon below $M_{\rm max} \sim 10^{20}\,$g. The upper part of the mass window should therefore be closed by other means.