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【Abstract】

The gigantic number of neutrinos emitted during a core-collapse supernova or a neutron-star merger can form a dense medium that experiences flavor oscillations collectively. Collective neutrino oscillations are typically studied with the mean-field theory which ignores the quantum entanglement among the neutrinos. In this talk, I will discuss how the entanglement between neutrinos through the forward-scattering Hamiltonian may affect the flavor evolution of the neutrino medium. Using the once-in-a-lifetime counter model, I will show that the medium refraction effect in the mean-field theory can be achieved through many distinct but weak forward scattering events. In the opposite limit, however, neutrinos rapidly lose their flavor identities through entanglement and the neutrino medium reaches the flavor equilibration which is determined by the lepton number conservation.