Quantify angular diffusion from M1 closure artifacts

Quantify the artificial angular diffusion introduced by the Minerbo closure in energy-integrated M1 neutrino transport by comparing its angular radiation fields with results from fully angle-dependent transport or Monte Carlo methods.

Background

The paper analyzes the angular structure of neutrino radiation from binary neutron-star mergers using an energy-integrated M1 moment scheme with the Minerbo closure. Although the dominant late-time quadrupolar geometry is attributed to macroscopic optical-depth gradients in the remnant–torus system, the authors note that M1 closures can produce ray-crossing artifacts when radiation beams from different emission surfaces intersect in optically thin regions.

Such artifacts may smooth the radiation field or alter minor higher-order multipoles. A dedicated comparison with fully angle-dependent transport or Monte Carlo calculations is therefore needed to determine whether, and to what extent, the reported fine angular features are numerical consequences of the moment closure.

References

Consequently, some fraction of the angular smoothing or minor higher-order multipole features in the optically thin limit could be influenced by the closure relation. While the dominant quadrupole geometry is robustly driven by the macroscopic optical depth gradients of the torus, future studies utilizing fully angle-dependent transport or Monte Carlo methods, e.g., , will be essential to definitively quantify any artificial angular diffusion introduced by the moment closure.

— Multipolar Neutrino Radiation in Binary Neutron Star Mergers: Angular Structure, Rotational Variability, and Implications for Electron Fraction  (2608.16275 - Çokluk et al., 17 Aug 2026) in Conclusions, final paragraph

It remains unclear how generic the success of a moment-based strategy is.

— Collective flavor conversion in dense neutrino plasmas  (2609.19256 - Fiorillo, 16 Sep 2026) in Section 7.3, Quantum moments