Speaker
Description
Ultralight Dark Matter (ULDM) is a compelling alternative to the WIMP paradigm, offering potential solutions to small-scale structure challenges through its wave-like behavior. A hallmark of ULDM is the presence of interference-induced overdensities, or "Extended Dark Objects" (EDOs), which arise naturally within the dark matter halo. In this talk, we present a method to constrain the ULDM mass and fraction using the observation of highly magnified stars near the caustics of giant arcs in galaxy clusters.
Utilizing the BBKS formalism to characterize the statistical properties of these overdensities, we calculate the expected optical depth for microlensing events. We demonstrate that sufficiently dense EDOs can significantly alter the magnification of background stars, such as the Icarus event (MACS J1149 Lensed Star 1), potentially leading to peak magnitudes that exceed observational thresholds. By comparing theoretical predictions with this extreme magnification event, we derive constraints on the ULDM parameter space, specifically the particle mass and the dark matter fraction. Our results highlight the power of caustic crossings in galaxy clusters as a high-resolution laboratory for testing the particle nature of dark matter.