Sterile Neutrinos: Reconciling Terrestrial Evidence with Cosmology

Tantalizing cosmological and terrestrial evidence suggests the number of light neutrinos may be greater than 3, however, tension between the various data sets remains. After reviewing some of the data, I will discuss several effects that could ease this tension by modifying the sterile neutrino contribution to the radiation abundance, including partial thermalization of the sterile states, and the effect of a nonzero neutrino mass.