Primordial black holes (PBHs) are a well-motivated dark-matter candidate that may have formed in the early Universe from the collapse of primordial density fluctuations. If PBHs constitute even a fraction of dark matter, they can be probed through gravitational microlensing. To test this possibility, we have been conducting microlensing observations of stars in the Andromeda galaxy (M31) with the Subaru Hyper Suprime-Cam (HSC).
In this talk, I will present the latest results from our Subaru HSC analysis, including both a reanalysis of previous observations and the analysis of newly acquired data, based on a new event-search pipeline designed to improve the sensitivity to PBH microlensing signals. The pipeline adopts a more flexible microlensing light-curve model, including finite-source effects, enabling improved fits to candidate events. I will also discuss how these candidates should be interpreted in the context of recent independent reanalyses of the Subaru HSC data and related microlensing results from other surveys.