Structure formation for light annihilating Dark Matter

Dark Matter (DM) is generally assumed to be made of weakly interacting massive particles. The latter are now embedded in the Cold Dark Matter (CDM) scenario. CDM does not necessarily mean collisionless DM though. In fact, DM with quite strong interactions may still appear as perfect CDM candidates. Alternatively DM particles with weak interactions may suffer from large collisional damping effects that make them looking alike Warm (or even Hot) Dark Matter (WDM) candidates. This is expected to be relevant, in particular, if DM is lighter than a proton. Light Dark Matter particles (LDMp) were introduced as an alternative to neutralinos. They become much more interesting after one realizes that they could potentially explain the 511 keV emission line detected and mapped by INTEGRAL/SPI in the center of the galaxy. Here, we study their consequences on structure formation.