Self-interacting Dark Matter

A theoretical model proposing that dark matter particles do not just feel gravity, but can also interact with each other through a new, non-gravitational force - a "dark force." This is in contrast to the standard Cold Dark Matter model, where particles are collisionless. The key idea is that these occasional interactions can transfer energy and momentum within dark matter halos. This can solve small-scale problems with the standard model, such as making dark matter halos less "cuspy" in their centers and bringing simulated satellite galaxy populations into better agreement with observations. It suggests a richer, more complex "dark sector" of physics, where dark matter might have its own interactions and light force carriers, creating a hidden world that only reveals itself through gravity.