Small-scale structure of cold dark matter

We investigate the clumping of cold dark matter (CDM) at small scales. If the CDM particle is the neutralino, we find that collisional damping during its kinetic decoupling from the radiation fluid and free streaming introduce a small-scale cut-off in the primordial power spectrum of CDM. This cut-off sets the scale for the very first CDM objects in the Universe, which we expect to have a mass of $\sim 10^{-12} M_\odot$. For non-thermal CDM candidates, such as axions, wimpzillas, or primordial black holes, the cosmological QCD transition might induce features in the primordial spectrum at similar mass scales.