Testing the Collisionless Nature of Dark Matter using Gravitational Lensing in Galaxy Clusters

Galaxy clusters are observed to be the most massive cosmic objects bound by gravity. The deep potential well of galaxy clusters indicates that their mass is dominated by electromagnetically invisible dark matter, which is found to make up about 85 per-cent of the total matter in the Universe. Gravitational lensing predicted by Einstein's theory of general relativity offers a powerful way to unlock the mysterious nature of dark matter. In this talk, we will discuss prospects for studying the dark matter distribution in galaxy clusters and constraining the nature of dark matter from combined strong and weak gravitational lensing. In particular, we will introduce and discuss a new method for constraining the self-interacting dark matter cross-section using the radial acceleration relation in galaxy clusters. By comparing the theoretical predictions derived from cosmological hydrodynamical simulations with deep lensing and X-ray observations in high-mass galaxy clusters, we will demonstrate the power of the cluster-scale radial acceleration relation for testing the collisionless nature of dark matter (Tam, Umetsu, Robertson, and McCarthy 2022, arXiv:2207.03506).