"Mere anarchy is loosed upon the world: Relic neutrinos (active and sterile), 7Li, N_eff, and Dark Matter"

Breakthroughs in experimental neutrino physics, impressive as these have been, raise many questions about new beyond-standard-model physics in the neutrino sector, and some of these are very difficult to address via the lab. However, observational cosmology is poised to lower the hammer and provide new probes of this physics. I will describe these probes/constraints and outline how new neutrino physics in some cases leads to testable predictions about observables like the radiation energy density at photon decoupling (parameterized by N_eff), neutrino "mass", and the primordial light element abundances. These, in turn, may give insights into, and even suggest, schemes for sterile neutrino dark matter production.