Neutrinos in Astrophysics and Cosmology: Theoretical Advanced Study
  Institute (TASI) 2020 Lectures
  I introduce the consequences of neutrino mass and mixing in the dense
environments of the early Universe and in astrophysical environments. Thermal
and matter effects are reviewed in the context of a two-neutrino formalism,
with methods of extension to multiple neutrinos. The observed large neutrino
mixing angles place the strongest constraint on cosmological lepton (or
neutrino) asymmetries, while new sterile neutrinos provide a wealth of possible
new physics, including lepton asymmetry generation as well as candidates for
dark matter. I also review cosmic microwave background and large-scale
structure constraints on neutrino mass and energy density. Lastly, I review how
X-ray astronomy has become a branch of neutrino physics in searches for
keV-scale sterile neutrino dark matter radiative decay.
