"Beyond Collisionless Dark Matter"

Abstract: There are long-standing hints from astrophysical observations that dark matter (DM) may not be collisionless, as is commonly assumed, but rather may possess a sizable cross section for scattering with other DM particles in halos. I discuss the evidence for self-interacting dark matter (SIDM), as well as recent progress in simulations and observations, and the particle physics implications of SIDM. Within the framework of minimal ''simplified'' models for SIDM, I describe how a variety of complementary probes, from astrophysics to terrestrial experiments, can explore SIDM.