Can we ignore the time dependence in matter-neutrino resonance?

In the vicinity of neutron star mergers (NSMs), it is possible for the neutrino self-interaction potential to cancel with the matter potential, leading to matter-neutrino resonance (MNR). MNR is one of the most interesting mechanisms by which neutrino flavor evolution can occur in dense astrophysical environments. Previous studies have typically assumed that the neutrino flavor field evolves to a steady state — a simplification also used in other self-interaction models, such as the neutrino-bulb model. Here, we perform reproducible calculations of MNR using both time-independent and time-dependent formalisms and show that they yield qualitatively different flavor survival probabilities. The time-independent approach produces unstable steady-state solutions that differ fundamentally from the dynamical behavior captured in time-dependent simulations. These results demonstrate that the steady-state assumption is generally invalid, and physical interpretations based on time-independent calculations of dense neutrino systems require re-evaluation.