The power spectrum of SUSY-CDM on subgalactic scales

The formation of large-scale structure is independent of the nature of the cold dark matter (CDM), however the fate of very small-scale inhomogeneities depends on the microphysics of the CDM particles. We investigate the matter power spectrum for scales that enter the Hubble radius well before matter-radiation equality, and follow its evolution until the time when the first inhomogeneities become non-linear. Our focus lies on weakly interacting massive particles (WIMPs), and as a concrete example we analyse the case when the lightest supersymmetric particle is a bino. We show that collisional damping and free-streaming of WIMPs lead to a matter power spectrum with a sharp cut-off at about 10(-6) M-circle dot and a maximum close to that cut-off. We also calculate the transfer function for the growth of the inhomogeneities in the linear regime. These three effects (collisional damping, free-streaming and gravitational growth) are combined to provide a WMAP normalized primordial CDM power spectrum, which could serve as an input for high-resolution CDM simulations. The smallest inhomogeneities typically enter the non-linear regime at a redshift of about 60.