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

Understand

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.