Robust integration of fast flavor conversions in classical neutrino transport

The quantum kinetic evolution of neutrinos in dense environments, such as the core-collapse supernovae or the neutron star mergers, can result in fast flavor conversion (FFC), presenting a significant challenge to achieving robust astrophysical modeling of these systems. Recent works that directly simulate the quantum kinetic transport of neutrinos in localized domains have suggested that the asymptotic outcome of FFCs can be modeled by simple analytical prescriptions. In this Letter, we incorporate the analytical prescriptions into global simulations that solve the classical neutrino transport equation including collisions and advection under spherical symmetry. We demonstrate excellent agreement between results obtained using this approach and those directly from the corresponding global quantum kinetic simulations. In particular, this effective method can also precisely capture the collisional feedback effect for cases where the FFC happens inside the neutrinosphere. Our work highlights that a robust integration of FFCs in classical neutrino transport used in astrophysical simulation can be feasible.