"Dark Matter Distinguished by Skewed Microlensing in the “Dragon Arc”"

Dark matter properties can be probed using lensed star transients observed near the critical curve of a galaxy cluster lens. In the “Dragon Arc”, these transients cluster preferentially inwards of the critical curve, where negative-parity images form. Ultra-massive dark matter halos would predict the opposite distribution. Quantum-interference-driven density modulations from ultra-light (~10⁻²² eV) axion-like particles reproduce the observed inward skewness, lending support to new physics scenarios beyond standard ultra-massive dark matter models.