Cosmology: small-scale issues

The abundance of dark matter satellites and subhalos, the existence of density cusps at the centers of dark matter halos and problems producing realistic disk galaxies in simulations are issues that have raised concerns about the viability of the standard cold dark matter (3CDM) scenario for galaxy formation. This paper reviews these issues and considers the implications for cold versus various varieties of warm dark matter (WDM). The current evidence appears to be consistent with standard 3CDM, although improving data may point toward a rather tepid version of 3WDM—tepid since the dark matter cannot be very warm without violating observational constraints. (This is a substantially updated and expanded version of my talk at the DM08 meeting at Marina Del Rey, arXiv:0902.2506.