Microlensing constraints on axion stars including finite lens and source size effects

TL;DR

This paper investigates how gravitational microlensing can detect axion star clumps, considering finite size effects, and derives constraints on axion properties from observational data, offering a new approach to dark matter detection.

Contribution

It provides a detailed microlensing analysis including finite lens and source size effects, constraining axion mass and self-interactions based on observational data.

Findings

Constraints on axion mass and clump density from microlensing data

Limits on the fraction of dark matter in axion clumps

Potential for microlensing to discover scalar dark matter structures

Abstract

A fraction of light scalar dark matter, especially axions, may organize into Bose-Einstein condensates, gravitationally bound clumps, "boson stars", and be present in large number in galactic halos today. We compute the expected number of gravitational microlensing events of clumps composed of the ordinary QCD axion and axion-like-particles and derive microlensing constraints from the EROS-2 survey and the Subaru Hyper Suprime-Cam observation. We perform a detailed lensing calculation, including the finite lens and source size effects in our analysis. We constrain the axion mass in terms of the fraction of dark matter collapsed into clumps, the individual clump densities, and the axion self-coupling. We also consider and constrain clumps composed of a generic scalar dark matter candidate with repulsive self-interactions. Our analysis opens up a new window for the potential discovery of dark matter.