Enhanced Small-Scale Structure in the Cosmic Dark Ages

Abstract: We consider the consequences of a matter power spectrum which rises on small scales until eventually being cutoff by microphysical processes associated with the particle nature of dark matter. Evolving the perturbations of a weakly interacting massive particle from before decoupling until deep in the nonlinear regime, we show that nonlinear structure can form abundantly at very high redshifts. In such a scenario, dark matter annihilation is substantially increased after matter-radiation equality. Furthermore, since the power spectrum can be increased over a broad range of scales, the first star forming halos may form earlier than usual as well. The next challenge is determining how early Universe observations may constrain such enhanced dark matter perturbations.