Halo Models of Large Scale Structure and Reliability of Cosmological N-Body Simulations

TL;DR

This paper critically examines halo models of large scale structure, highlighting limitations of N-body simulations in reliably defining halos as smooth entities, and suggests alternative approaches for consistent halo definitions.

Contribution

It provides a detailed analysis of the assumptions behind halo models and N-body simulations, proposing the need for alternative halo definitions based on scale or baryonic physics.

Findings

N-body simulations are not fully reliable at scales where halos appear.

Standard halo definitions based on smooth dark matter distributions are questionable.

Alternative halo definitions may involve grainy structures or baryonic physics.

Abstract

Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos, it is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics.