# Primordial Black Hole Microlensing: The Einstein Crossing Time Distribution

## TL;DR

This paper investigates how the distribution of microlensing event durations can be used to detect or constrain primordial black holes in the Milky Way, especially in light of recent gravitational wave discoveries.

## Contribution

It provides a simple calculation showing how the Einstein crossing time distribution varies with different primordial black hole abundances in the galaxy.

## Key findings

- tE distribution differs significantly with PBH presence
- Models without PBHs do not match observed tE distributions
- The method can statistically distinguish PBH contributions

## Abstract

Gravitational microlensing is one of the few means of finding primordial black holes (PBHs), if they exist. Recent LIGO detections of 30 Msun black holes have re-invigorated the search for PBHs in the 10-100 Msun mass regime. Unfortunately, individual PBH microlensing events cannot easily be distinguished from stellar lensing events from photometry alone. However, the distribution of microlensing timescales (tE, the Einstein radius crossing time) can be analyzed in a statistical sense using models of the Milky Way with and without PBHs. While previous works have presented both theoretical models and observational constrains for PBHs (e.g. Calcino et al. 2018; Niikura et al. 2019), surprisingly, they rarely show the observed quantity -- the tE distribution -- for different abundances of PBHs relative to the total dark matter mass (fPBH). We present a simple calculation of how the tE distribution changes between models with and without PBHs.