# Astrophysical uncertainties on stellar microlensing constraints on multi-Solar mass primordial black hole dark matter

## TL;DR

This paper examines how astrophysical uncertainties, especially in velocity distributions, affect stellar microlensing constraints on multi-Solar mass primordial black holes as dark matter, highlighting the importance of these uncertainties in constraint calculations.

## Contribution

It analyzes the impact of astrophysical uncertainties on microlensing constraints, showing that velocity distribution variations can significantly weaken the constraints on primordial black hole dark matter.

## Key findings

- Constraints vary by an order of magnitude with velocity dispersion changes.
- Reducing velocity dispersion weakens microlensing constraints.
- Astrophysical uncertainties are crucial for accurate constraint assessments.

## Abstract

There has recently been interest in multi-Solar mass Primordial Black Holes (PBHs) as a dark matter (DM) candidate. There are various microlensing, dynamical and accretion constraints on the abundance of PBHs in this mass range. Taken at face value these constraints exclude multi-Solar mass PBHs making up all of the DM for both delta-function and extended mass functions. However the stellar microlensing event rate depends on the density and velocity distribution of the compact objects along the line of sight to the Magellanic Clouds. We study the dependence of the constraints on the local dark matter density and circular speed and also consider models where the velocity distribution varies with radius. We find that the largest mass constrained by stellar microlensing can vary by an order of magnitude. In particular the constraints are significantly weakened if the velocity dispersion of the compact objects is reduced. The change is not sufficiently large to remove the tension between the stellar microlensing and dynamical constraints. However this demonstrates that it is crucial to take into account astrophysical uncertainties when calculating and comparing constraints. We also confirm the recent finding that the tension between the constraints is in fact increased for realistic, finite width mass functions.