Gravitational microlensing by dressed primordial black holes

TL;DR

This paper investigates how dark matter minihalos around primordial black holes affect gravitational microlensing signals, leading to improved constraints on PBH abundance and their potential role as dark matter.

Contribution

It provides a detailed analysis of microlensing effects by dressed PBHs with minihalos and demonstrates how these effects can tighten constraints on PBH dark matter.

Findings

Minihalo size influences microlensing asymptotic behavior.

Density distribution significantly affects microlensing when halo and Einstein radius are comparable.

Constraints on PBH abundance are strengthened, especially in the asteroid mass window.

Abstract

The accretion of dark matter around the primordial black holes (PBHs) could lead to the formation of surrounding minihalos, whose mass can be several orders of magnitude higher than the central PBH mass. The gravitational microlensing produced by such dressed PBHs could be quite different from that of the bare PBHs, which may significantly affect the constraints on the PBH abundance. In this paper, we study the gravitational microlensing produced by dressed PBHs in detail. We find that all the microlensing effects by dressed PBHs have asymptotic behavior depending on the minihalo size, which can be used to predict the microlensing effects by comparing the halo size with the Einstein radius. When the minihalo radius and the Einstein radius are comparable, the effect of the density distribution of the halo is significant to the microlensing. Applying the stellar microlensing by dressed PBHs to the data of the Optical Gravitational Lensing Experiment and Subaru/HSC Andromeda observations, we obtain the improved constraints on the PBH abundance. It shows that the existence of dark matter minihalos surrounding PBHs can strengthen the constraints on the PBH abundance from stellar microlensing by several orders, and can shift the constraints to the well-known asteroid mass window where PBHs can constitute all the dark matter.