Abstract:
So far, only gravitational signatures of dark matter have been observed. However, in many theories — in particular, all models which could be observed in laboratory experiments — dark matter has extra interactions with the Standard Model and/or itself. In this seminar, I’ll talk about the unusual behaviour that can arise if these interactions are long-ranged. While most computations of dark matter scattering treat different particles as independent, long-range interactions can make coherent scattering much more important. Most dramatically, small perturbations can be amplified exponentially — the analogue of electromagnetic plasma instabilities. These instabilities may place very strong limits on the dark matter’s interaction strength, or conversely, allow very tiny couplings to give observational signatures. Dark matter models which encounter these effects include popular experimental targets such as millicharged DM, and DM interacting through a kinetically mixed dark photon.