An Excessive Core Collapse in Nbody Cosmological simulations

Abstract

The particle mass used in cosmology N-body simulations is close to 10 8 M ⊙ , which is about 10 65 times larger than the GeV scale expected in particle physics. However, self-gravity interacting particle systems made up of different particle number and mass have different statistical and dynamical properties. Here we demonstrate that, due to this particle number and mass difference, the nowaday cosmology N-body simulations can have introduced an excessive core collapse process, especially for the small halos at high redshift. Such dynamical effect introduces an excessive cuspy center for these small halos, and it implies a possible connection to the so called "small scale crisis" for CDM models. Our results show that there exist a physical limit in cosmological simulations, by using about 10 3 particles to describe smallest halos, and we provide a simple suggestion based on it to relieve those effects from the bias.