NADA-FLD: A General Relativistic, Multi-dimensional Neutrino-hydrodynamics Code Employing Flux-limited Diffusion

Understand

We present the new code NADA-FLD to solve multi-dimensional neutrino-hydrodynamics in full general relativity (GR) in spherical polar coordinates.

• The energy-dependent neutrino transport assumes the flux-limited diffusion (FLD) approximation and evolves the neutrino energy densities measured in the frame comoving with the fluid.
• Operator splitting is used to avoid multi-dimensional coupling of grid cells in implicit integration steps involving matrix inversions.
• Terms describing lateral diffusion and advection are integrated explicitly using the Allen-Cheng or the Runge-Kutta-Legendre method, which remain stable even in the optically thin regime.