Observations have uncovered a new type of gravitational lensing phenomenon that can be utilized to address fundamental physics questions: in galaxy cluster strong lensing systems, background galaxies straddle the lensing caustic and stars near the caustic can be individually detectable to optical/IR telescopes (as in the case of a recent detection by the HST) thanks to the extreme magnification. I discuss how we can use caustic-crossing stars to probe small subhalos or other small-scale granularity in the cluster's halo beyond the reach of existing methods, thus constraining the microscopic nature of the dark matter. I also discuss the prospect of this method with the forthcoming JWST or with the next-generation giant ground-based optical/IR telescopes.

BIO
Dr. Liang Dai was a Peking University undergraduate in the School of Physics. Dr. Dai received his PhD in Physics at the Johns Hopkins University under the supervision of Prof. Marc Kamionkowski. Afterwards, he was awarded the NASA Einstein Fellowship to further his research. Currently, he is a Postdoctoral Member at the Institute for Advanced Study of Princeton. Dr. Dai has a wide range of interests in theoretical astrophysics. He has done many works on cosmology related to the cosmic microwave background and the cosmic large-scale structure. His latest research focuses include gravitational lensing, astrophysical gravitational waves, and 21cm cosmology.