Elastic Scattering in General Relativistic Ray Tracing for Neutrinos

TL;DR

This paper introduces a covariant ray tracing algorithm for neutrinos in general relativistic spacetimes, incorporating elastic scattering effects to improve accuracy in modeling neutrino transport in astrophysical phenomena.

Contribution

The paper presents a novel covariant ray tracing method that includes elastic scattering of neutrinos, enhancing the realism of neutrino transport simulations in curved spacetimes.

Findings

Elastic scattering significantly alters neutrino fluxes and spectra.

The method effectively handles regimes from optically thick to thin.

Application to neutron star mergers reveals different neutrino behaviors with scattering included.

Abstract

We present a covariant ray tracing algorithm for computing high-resolution neutrino distributions in general relativistic numerical spacetimes with hydrodynamical sources. Our formulation treats the very important effect of elastic scattering of neutrinos off of nuclei and nucleons (changing the neutrino's direction but not energy) by incorporating estimates of the background neutrino fields. Background fields provide information about the spectra and intensities of the neutrinos scattered into each ray. These background fields may be taken from a low-order moment simulation or be ignored, in which case the method reduces to a standard state-of-the-art ray tracing formulation. The method handles radiation in regimes spanning optically thick to optically thin. We test the new code, highlight its strengths and weaknesses, and apply it to a simulation of a neutron star merger to compute neutrino fluxes and spectra, and to demonstrate a neutrino flavor oscillation calculation. In that environment, we find qualitatively different fluxes, spectra, and oscillation behaviors when elastic scattering is included.