Testing standard perturbation theory and the Eulerian local biasing scheme against N-body simulations

TL;DR

This paper evaluates third-order standard perturbation theory's accuracy in modeling non-linear structure formation and assesses the Eulerian local bias model's effectiveness in reconstructing halo distributions from simulations.

Contribution

It introduces a novel numerical method to compare SPT with N-body simulations and evaluates the bias model's ability to replicate halo clustering properties.

Findings

SPT agrees well with simulations for smoothing scales above 8 Mpc/h up to redshift 0.

A fitting formula accurately relates linear and non-linear density contrasts from z=0 to z=10.

The Eulerian local bias model partially captures halo distribution but has limitations.

Abstract

We test third-order standard perturbation theory (SPT) as an approximation to non-linear cosmological structure formation. A novel approach is used to numerically calculate the three-dimensional dark matter density field using SPT from the initial conditions of two high-resolution cosmological simulations. The calculated density field is compared to the non-linear dark matter field of the simulations both point-by-point and statistically. For smoothing scales above 8 Mpc/h it shows a good agreement up to redshift 0. We present a simple fitting formula to relate the linear and non-linear density contrast that accurately recovers the non-linear time evolution for 0 <= z <= 10 at the per cent level. To address the problem of biasing between the matter field and the haloes identified in the simulation, we employ the Eulerian local bias model (ELB), including non-linear bias up to the third order. The bias parameters are obtained by fitting a scatter plot of halo and matter density (both from the simulation and from SPT). Using these bias parameters, we can reconstruct the halo density field. We find that this reconstruction is not able to capture all the details of the halo distribution. We investigate how well the large scale bias can be described by a constant and if it corresponds to the linear bias parameter b_1 of the local bias model. We also discuss how well the halo-halo power spectrum and the halo-mass cross spectrum from the reconstructed halo density field agree with the corresponding statistics from the simulation. The results show that while SPT is an excellent approximation for the matter field for suitably large smoothing scales even at redshift 0, the ELB model can only account for some of the properties of the halo density field.