Reducing Noise in Cosmological N-body Simulations with Neutrinos

TL;DR

This paper introduces a novel method for initializing cosmological N-body simulations with massive neutrinos, significantly reducing shot noise and enabling detailed studies of neutrino clustering and velocity distributions across cosmic time.

Contribution

The authors develop a new approach to generate initial conditions for neutrino particles in simulations, markedly decreasing shot noise and improving the accuracy of density and velocity field evolution.

Findings

Shot noise in neutrino power spectrum reduced by over 10^7 at high redshift.

Improved accuracy in total matter power spectrum on large scales.

Enables detailed analysis of neutrino clustering and velocity distribution evolution.

Abstract

We present a new method for generating initial conditions for numerical cosmological simulations in which massive neutrinos are treated as an extra set of N-body (collisionless) particles. It allows us to accurately follow the density field for both Cold Dark Matter (CDM) and neutrinos at both high and low redshifts. At high redshifts, the new method is able to reduce the shot noise in the neutrino power spectrum by a factor of more than $10^7$ compared to previous methods, where the power spectrum was dominated by shot noise at all scales. We find that our new approach also helps to reduce the noise on the total matter power spectrum on large scales, whereas on small scales the results agree with previous simulations. Our new method also allows for a systematic study of clustering of the low velocity tail of the distribution function of neutrinos. This method also allows for the study of the evolution of the overall velocity distribution as a function of the environment determined by the CDM field.