An Overview of Modern Dark Complexity

Abstract: The possibility of dark matter being a complex dark sector with several stable particles interacting via their own set of forces has received increased attention in recent years. This is because it became clear that such possibilities are motivated by theoretical considerations like solutions to the electroweak hierarchy problem, and because modern astrophysical techniques that are necessary to understand nontrivial observable predictions are being applied to these scenarios. I will give an idiosyncratic overview of some recent advances in understanding dark complexity in theory, simulations and observations from the cosmological scale down to galaxies, stars and direct detection experiments. A common benchmark model for dark complexity is atomic dark matter, where a fraction of dark matter is made up of dark protons and dark electrons interacting via a form of dark electromagnetism with coupling constants and masses regarded as free parameters, but this is a suitable stand-in for more complete scenarios that may additionally feature things like dark nuclear physics.