Neutrinos in Non-linear Structure Formation - a Simple SPH Approach

TL;DR

This paper introduces a simple, effective SPH-based method for incorporating massive neutrinos into N-body simulations by modeling neutrino free-streaming as a redshift-dependent sound speed, achieving comparable accuracy to complex hybrid methods.

Contribution

The paper proposes a novel, simplified approach to simulate massive neutrinos in N-body simulations using an effective sound speed, facilitating easier implementation in existing codes.

Findings

Accurately computes the total matter power spectrum with simpler methods.

Fails to precisely model the neutrino power spectrum at small scales.

Provides an easy update for Gadget-2 with the new neutrino approximation.

Abstract

We present a novel method for implementing massive neutrinos in N-body simulations. Instead of sampling the neutrino velocity distribution by individual point particles we take neutrino free-streaming into account by treating it as an effective redshift dependent sound speed in a perfect isothermal fluid, and assume a relation between the sound speed and velocity dispersion of the neutrinos. Although the method fails to accurately model the true neutrino power spectrum, it is able to calculate the total matter power spectrum to the same accuracy as more complex hybrid neutrino methods, except on very small scales. We also present an easy way to update the publicly available Gadget-2 version with this neutrino approximation.