Neutrinos and the Supernova Origin of the Elements

Intense fluxes of neutrinos are emitted by the hot neutron star produced in a supernova. The average supernova neutrino energies satisfy a robust hierarchy 〈Eνe〉 < 〈Eν̄e〉 < 〈Eνμ(τ)〉 ≈ 〈Eν̄μ(τ)〉. The νe and ν̄e capture reactions on neutrons and protons, respectively, provide heating to drive a wind from the hot neutron star. The same reactions also determine the neutron-richness of the wind material. Nucleosynthesis via rapid neutron capture, the r-process, may occur in the wind material as it expands away from the neutron star. The neutron-richness of the wind material, and hence, the r-process nucleosynthesis therein, are sensitive to mixing between νμ(τ)/ν̄μ(τ) and νe/ν̄e (or sterile neutrinos νs/ν̄s) at the level of sin 2 2θ ∼ 10 −4 for δm ∼ 1 eV . Indirect arguments and direct tests for the supernova origin of the r-process elements are discussed with a goal to establish supernova r-process nucleosynthesis as an important probe for neutrino mixing.