Asymptotic and Dynamical States of Collective Neutrino Flavor Conversions in Astrophysical Environments

Collective neutrino flavor conversions can strongly reshape the neutrino radiation fields in core-collapse supernovae and neutron star mergers. Yet, their nonlinear dynamics and asymptotic outcomes remain poorly constrained. We present a theoretical and computational framework that bridges quasi-static analysis with reduced transport modeling of flavor conversions in dense neutrino gases. Using a three-flavor BGK (Bhatnagar–Gross–Krook) scheme, we characterize the asymptotic flavor states and relaxation timescales for various angular and spectral configurations. The method has been implemented in core-collapse supernova simulations employing full Boltzmann neutrino transport, demonstrating its compatibility with large-scale numerical frameworks. Our results highlight the emergence of dynamical equilibria and their potential feedback on neutrino heating and nucleosynthesis in astrophysical outflows.