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.