A practical guide to a moment approach for neutrino transport in numerical relativity

Abstract

The development of a neutrino moment based radiative-transfer code to simulate binary neutron-star mergers can easily become an obstacle path because of the numerous ways in which the solution of the equations may fail. We describe the implementation of the grey M1 scheme in our fully general-relativistic magnetohydrodynamics code and detail those choices and strategies that could lead either to a robust scheme or to a series of failures. In addition, we present new tests designed to show the consistency and accuracy of our code in conditions that are similar to realistic merging conditions and introduce a new, publicly available, benchmark based on the head-on collision of two neutron stars. This test, which is computationally less expensive than a complete merging binary but has all the potential pitfalls of the full scenario, can be used to compare future implementations of M1 schemes with the one presented here.

General-relativistic Radiation Transport Scheme in Gmunu. II. Implementation of Novel Microphysical Library for Neutrino Radiation—Weakhub

“…Typical neutrino opacities utilized for cooling and nucleosynthesis in BNS postmerger systems are energy-averaged and primarily based on the calculations of Ruffert et al (1996) and Ardevol-Pulpillo et al (2019). Recent BNS simulations have been performed with these opacities (Foucart et al 2015(Foucart et al , 2016Radice et al 2022;Musolino & Rezzolla 2024). Specifically, the energy-averaged absorption opacity is determined by averaging an energy-dependent neutrino distribution function (assuming in LTE) with the energy-dependent opacity, which is calculated under elastic approximation and without any corrections (see equation (B13) in Ardevol-Pulpillo et al 2019).…”

“…Examples include the calculations of neutrino opacities for β-processes and scattering with matter (Bruenn 1985;Burrows et al 2006), the neutrino production rates of the e − e + pair annihilation and nucleon-nucleon Bremsstrahlung (Bruenn 1985;Hannestad & Raffelt 1998;Pons et al 1998;Misiaszek et al 2006). These calculations are applied as the collisional source terms in the Boltzmann equation for different simplified neutrino radiative transfer schemes utilized in the modeling of CCSNe (Bruenn 1985;Rampp & Janka 2002;Liebendörfer et al 2005;Müller et al 2010;Just et al 2015;O'Connor 2015;Kuroda et al 2016) and compact binary coalescence (Ruffert et al 1997;Sekiguchi et al 2015;Foucart et al 2015Foucart et al , 2016aFoucart et al , 2016bFoucart et al , 2016Radice et al 2022;Musolino & Rezzolla 2024).…”