Effects of Different Closure Choices in Core-Collapse Supernova Simulations

TL;DR

This study evaluates how different closure relations in the two-moment neutrino transport method affect core-collapse supernova simulations, finding that second-order closures have more impact than third-order ones, but overall effects are minor compared to physical input uncertainties.

Contribution

It systematically compares the effects of various closure choices on supernova simulation results using the Fornax code, highlighting the relative importance of closure order.

Findings

Second-order closures have larger effects than third-order closures.

Deviations in Eddington factors do not correlate directly with physical quantity deviations.

Closure choice effects are small compared to uncertainties in physical inputs.

Abstract

The two-moment method is widely used to approximate the full neutrino transport equation in core-collapse supernova (CCSN) simulations, and different closures lead to subtle differences in the simulation results. In this paper, we compare the effects of closure choices on various physical quantities in 1D and 2D time-dependent CCSN simulations with our multi-group radiation hydrodynamics code Fornax. We find that choices of the 3rd-order closure relations influence the time-dependent simulations only slightly. Choices of the 2nd-order closure relation have larger consequences than choices of the 3rd-order closure do, but these are still small compared to the remaining variations due to ambiguities in some physical inputs such as the nuclear equation of state. We also find that deviations in Eddington factors are not monotonically related to deviations in physical quantities, which means that simply comparing the Eddington factors does not inform one concerning which closure is better.