  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 (LambdaCDM) scenario for
galaxy formation. This article reviews these issues, and considers the
implications for cold vs. various varieties of warm dark matter (WDM). The
current evidence appears to be consistent with standard LambdaCDM, although
improving data may point toward a rather tepid version of LambdaWDM -- tepid
since the dark matter cannot be very warm without violating observational
constraints.
