Dark matter makes up most of the matter in the Universe, but its microscopic nature remains unknown. One way to learn about it is to measure how dark matter is distributed on scales much smaller than galaxies, where different models can make very different predictions. In this talk, I will discuss how strongly lensed stars behind galaxy clusters can provide a new probe of this small-scale structure. Stars that lie close to a gravitational-lensing caustic produce multiple images whose positions are exceptionally sensitive to small clumps of dark matter in the lensing cluster. Rather than attempting to identify each clump individually, we can use the correlated shifts that they produce in many stellar images to measure the statistical properties of the underlying dark-matter distribution. I will show how these correlations encode the spectrum of dark-matter fluctuations, and how existing JWST observations can already constrain departures from cold dark matter on remarkably small scales, corresponding to characteristic masses of order 10^5 solar masses.
Zoom Meeting: https://icts-res-in.zoom.us/j/92159106696?pwd=ysuR6vXboAbFa8L84M2w8bQKageNA7.1
Meeting ID: 921 5910 6696
Passcode: 202050