EMU: A PIC Approach to Neutrino Transport with Flavor Transformation

Simulations of neutron star mergers and supernovae show that the classical neutrino radiation field evolves toward a flavor-unstable configuration, even in the presence of collisions. This raises significant uncertainties in classical neutrino flavor path and underscores the need for a quantum kinetic approach. Allowing the neutrino field to change flavor, rather than evolving each flavor independently, can impact the dynamics and nucleosynthesis of supernovae and mergers. Outputs from classical models suggest that flavor conversion occurs on timescales extremely shorter than fluid changes, making it difficult to solve with current computational methods and approximations. A potential solution lies in the idea that the neutrino field may evolve at the edge of flavor instability, rather than in the highly unstable state suggested by classical models. To address this problem, I present recent advancements and simulations with EMU, a particle-in-cell based neutrino transport code that simulates flavor transformations in supernovae and merger environments, incorporating neutrino oscillations due to non-zero masses, MSW effects, self-interactions, and nucleon absorption and emission.