Speaker
Description
A future Galactic core-collapse supernova will produce high-statistics neutrino signals in water Cherenkov, liquid argon, and liquid scintillator detectors. Interpreting these signals requires reliable modeling of neutrino flavor transformation inside the dense supernova environment. In regions near the proto-neutron star, neutrino–neutrino forward scattering induces collective flavor evolution, leading to nonlinear instabilities that can significantly modify the emitted flavor composition before standard matter and vacuum oscillations dominate.
Collective flavor instabilities include both fast flavor instabilities (FFIs)—driven by angular crossings of the neutrino lepton number distribution—and collisional flavor instabilities (CFIs), which arise from the interplay between neutrino–matter scattering processes and flavor coherence. These instabilities grow on scales set by the neutrino self-interaction potential, much shorter than vacuum oscillation lengths, and can lead to rapid flavor conversion largely independent of small vacuum mixing parameters. FFIs are expected in regions near and above the neutrinosphere where forward-peaked angular distributions of neutrinos and antineutrinos generate crossings in the electron lepton number profile. In contrast, CFIs operate in regimes where neutrino collisions remain significant, linking flavor conversion directly to transport physics and potentially enabling flavor transformation deeper in the decoupling region than previously anticipated.
The nonlinear and multi-angle structure of collective flavor evolution makes direct implementation in multidimensional supernova simulations computationally challenging. We present a computationally efficient framework to determine the late-time flavor configuration resulting from collective instabilities within a three-flavor description. By exploiting the separation between rapid flavor equilibration and slower hydrodynamical evolution, the method predicts the asymptotic flavor state without resolving the full microscopic dynamics. Comparisons with multi-angle calculations demonstrate robust agreement across both collisionless and collisional instability regimes.
We evaluate how collective flavor instabilities reshape emergent neutrino spectra and discuss implications for observable signals in large-scale detectors. Our results indicate that both fast and collisional regimes can alter flavor-dependent luminosities and energy distributions, with measurable consequences for event rates and flavor sensitivity in a future Galactic supernova burst. This work provides a practical pathway toward incorporating collective flavor physics—including collisional effects—into supernova modeling and detector signal forecasts, helping reduce theoretical uncertainties in multimessenger neutrino astronomy.