Hot Dark Matter
	• E.g., neutrinos with rest mass on order of eV. • Highly relativistic when they decouple (around transition from radiation to matter domination) • Does NOT create large perturbations in the background radiation (good!). • Accounts for “cellular structure” seen. • Predicts the largest scale structures grow first • Fails to predict correlation functions on the right scales and galaxies form very late (bad!).