Connecting small-scale to large-scale structures of fast neutrino-flavor conversion

We present a systematic study of fast neutrino-flavor conversion (FFC) with both small-scale and large-scale numerical simulations in spherical symmetry. find that FFCs can, general, reach quasisteady state, these features the nonlinear phase are not characterized by growth rate FFC instability but rather angular structures electron neutrino lepton number (ELN) heavy one. Our result suggests neutrinos can almost flavor equipartition even cases low (e.g., shallow ELN crossing) narrow regions (in momentum space) where conversions occur vigorously. This shows heavy-neutrino distributions cannot provide sufficient information to determine total amount antineutrinos all flavors. Based on results our simulations, we new approximate scheme is designed so one easily incorporate effects existing classical transport codes for core-collapse supernova binary neutron star merger. The has an ability capture key state without solving quantum kinetic transport, which will serve facilitate access merger theorists.