Neutrinos and Dark Matter

In these lectures I highlight some key features of massive neutrinos in the context of cosmology. I first review the thermal history and the free-streaming kinematics of the uniform cosmic background neutrinos. I then describe how fluctuations in the phase space distributions of neutrinos and other particles arise and evolve after neutrino decoupling according to the linear perturbation theory of gravitational instability. The different clustering properties of massive neutrinos (aka hot dark matter) and cold dark matter are contrasted. The last part discusses the nonlinear stage of gravitational clustering and highlights the effects of massive neutrinos on the formation of cosmological structure.