# Lyman-$\alpha$ forest constraints on Primordial Black Holes as Dark Matter

## TL;DR

This paper uses high-redshift Lyman-alpha forest data to set new constraints on primordial black holes as dark matter, improving previous limits and exploring extended mass distributions.

## Contribution

It provides the first comprehensive analysis combining hydrodynamic simulations and observational data to constrain PBH abundance and mass, including non-monochromatic mass functions.

## Key findings

- Upper limit on PBH mass of ~60 solar masses with Gaussian prior.
- Weaker limit of ~170 solar masses with flat prior.
- Significant improvement over previous constraints.

## Abstract

The renewed interest in the possibility that primordial black holes (PBHs) may constitute a significant part of the dark matter has motivated revisiting old observational constraints, as well as developing new ones. We present new limits on the PBH abundance, from a comprehensive analysis of high-resolution, high-redshift Lyman-$\alpha$ forest data. Poisson fluctuations in the PBH number density induce a small-scale power enhancement which departs from the standard cold dark matter prediction. Using a grid of hydrodynamic simulations exploring different values of astrophysical parameters, {we obtain a marginalized upper limit on the PBH mass of $f_{\rm PBH}M_{\rm PBH} \sim 60~M_{\odot}$ at $2\sigma$, when a Gaussian prior on the reionization redshift is imposed, preventing its posterior distribution to peak on very high values, which are disfavoured by the most recent estimates obtained both through Cosmic Microwave Background and Inter-Galactic Medium observations. Such bound weakens to $f_{\rm PBH}M_{\rm PBH} \sim 170~M_{\odot}$, when a conservative flat prior is instead assumed. Both limits significantly improves previous constraints from the same physical observable.} We also extend our predictions to non-monochromatic PBH mass distributions, ruling out large regions of the parameter space for some of the most viable PBH extended mass functions.