Self-Interacting Dark Matter (SIDM)

Self-Interacting Dark Matter (SIDM) fixes a key cold dark matter flaw: galaxy centers show flatter density profiles than predicted, not the expected dense cores. SIDM proposes dark matter particles scatter with an interaction strength of about 1 cm²/g, as simulated by UC Irvine and Max Planck teams. These simulations match observations 30% better than collisionless models, but the required strength remains debated, making SIDM a strong yet not definitive alternative to #1 WIMPs. The benchmark interaction cross-section of 0.1 cm²/g is derived from cluster collisions like the Bullet Cluster.