Understanding the nature of dark matter is one of the most profound scientific challenges of the modern era. The compelling body of evidence has motivated multi-billion-euro experiments aimed at discovering new particles and uncovering new physics. Yet, despite extraordinary efforts, the nature of dark matter remains unknown.

 

Testing the nature of dark matter means testing its interactions beyond that of gravity, in particular those between Standard Model particles and dark matter via the four known forces. However, in the absence of any detection, new, exotic couplings are becoming increasingly interesting, including the dark matter self-interaction.

 

In this talk I will navigate the building body of evidence for dark matter with a non-zero self-interaction. I will show how a velocity-dependent cross-section is able to explain a wide range of astrophysical observations and is quickly becoming a leading model for dark matter. Finally I will look to the future and explore how new space-based telescopes are on the cusp of delivering paradigm shifting insights in to the nature of dark matter.