Simulating nonlinear cosmological structure formation with massive neutrinos

TL;DR

This paper introduces a hybrid simulation method for cosmologies with massive neutrinos, reducing shot noise and enabling detailed analysis of neutrino effects on large-scale structure, especially void bias.

Contribution

A novel combined particle-fluid simulation approach for massive neutrinos that minimizes shot noise and accurately models their impact on cosmic structure formation.

Findings

Massive neutrinos induce scale-dependent bias in cosmic voids.

The method effectively reduces shot noise in neutrino simulations.

Void bias behavior can be modeled with a simple spherical expansion.

Abstract

We present a new method for simulating cosmologies that contain massive particles with thermal free streaming motion, such as massive neutrinos or warm/hot dark matter. This method combines particle and fluid descriptions of the thermal species to eliminate the shot noise known to plague conventional N-body simulations. We describe this method in detail, along with results for a number of test cases to validate our method, and check its range of applicability. Using this method, we demonstrate that massive neutrinos can produce a significant scale-dependence in the large-scale biasing of deep voids in the matter field. We show that this scale-dependence may be quantitatively understood using an extremely simple spherical expansion model which reproduces the behavior of the void bias for different neutrino parameters.