Constraints on Long-Range Interactions of Dark Matter

There are a variety of experimental and astrophysical constraints on non-gravitational interactions of dark matter, both with itself and with the Standard Model. Most of these constraints assume that such interactions are short-ranged, however, with individual dark matter particles interacting with individual dark matter or Standard Model particles. It is also possible, for dark matter to have weak but long-ranged interactions, potentially resulting in collective interaction effects. I will present a variety of constraints on such interactions, focusing on two main examples: First, long-ranged self-interactions of dark matter would modify the results of the Bullet Cluster collision, either by separating the dark matter from the galaxies or by modifying the observed collision velocity of the intracluster gas. Notably, while these effects have been considered previously in the infinite-range limit, they remain significant at finite ranges due to the presence of dark matter density gradients. Second, I will present new constraints on dark matter-Standard Model interactions based on observations of ultrafaint dwarf galaxies, where interactions with ranges above O(mpc) and strengths of at least O(100) times gravity could significantly slow stars through enhanced dynamical friction.