Supernova Simulations with Boltzmann Neutrino Transport: A Comparison of Methods

TLDR

Accurate neutrino transport has been incorporated into spherically symmetric core‑collapse simulations, yet independent groups have adopted fundamentally different numerical methods to solve the Boltzmann neutrino transport equation. The study directly compares the AGILE‑BOLTZTRAN and VERTEX neutrino radiation‑hydrodynamics codes to test their implementations and establish a data basis for future supernova code verification. AGILE‑BOLTZTRAN solves the Boltzmann equation directly using an implicit, general‑relativistic discrete‑angle method on an adaptive grid with second‑order TVD advection, while VERTEX couples a variable Eddington factor approach with an explicit moving‑grid, high‑order Riemann solver and incorporates relativistic effects through an effective gravitational potential. The simulations confirm that spherically symmetric models with standard microphysics do not explode via the delayed neutrino‑driven mechanism, as demonstrated in 13 M☉ Newtonian and 15 M☉ relativistic gravity core‑collapse runs.

Abstract

Accurate neutrino transport has been built into spherically symmetric simulations of stellar core collapse and postbounce evolution. The results of such simulations agree that spherically symmetric models with standard microphysical input fail to explode by the delayed, neutrino-driven mechanism. Independent groups implemented fundamentally different numerical methods to tackle the Boltzmann neutrino transport equation. Here we present a direct and detailed comparison of such neutrino radiation-hydrodynamics simulations for two codes, AGILE-BOLTZTRAN of the Oak Ridge-Basel group and VERTEX of the Garching group. The former solves the Boltzmann equation directly by an implicit, general relativistic discrete-angle method on the adaptive grid of a conservative implicit hydrodynamics code with second-order TVD advection. In contrast, the latter couples a variable Eddington factor technique with an explicit, moving-grid, conservative high-order Riemann solver with important relativistic effects treated by an effective gravitational potential. The presented study is meant to test our neutrino radiation-hydrodynamics implementations and to provide a data basis for comparisons and verifications of supernova codes to be developed in the future. Results are discussed for simulations of the core collapse and postbounce evolution of a 13 M☉ star with Newtonian gravity and a 15 M☉ star with relativistic gravity.