Simulating the Cosmic Neutrino Background using Collisionless Hydrodynamics

TL;DR

This paper introduces a novel collisionless hydrodynamics method to simulate the cosmic neutrino background efficiently, accurately capturing neutrino perturbations while significantly reducing computational memory requirements.

Contribution

The authors develop a new shell-based hydrodynamic approach for simulating cosmic neutrinos that improves efficiency and accuracy over traditional N-body methods.

Findings

Neutrino perturbations are accurately resolved up to k~1 h/Mpc.

Memory usage is reduced by up to 1000 times compared to traditional methods.

The method matches linear theory and free particle evolution.

Abstract

The cosmic neutrino background is an important component of the Universe that is difficult to include in cosmological simulations due to the extremely large velocity dispersion of neutrino particles. We develop a new approach to simulate cosmic neutrinos that decomposes the Fermi-Dirac phase space into shells of constant speed and then evolves those shells using hydrodynamic equations. These collisionless hydrodynamic equations are chosen to match linear theory, free particle evolution and allow for superposition. We implement this method into the information-optimized cosmological $N$-body code CUBE and demonstrate that neutrino perturbations can be accurately resolved to at least $k\sim1\ h/$Mpc. This technique allows for neutrino memory requirements to be decreased by up to $\sim 10^3$ compared to traditional $N$-body methods.