Validating galaxy clustering models with Fixed & Paired and Matched-ICs simulations: application to Primordial Non-Gaussianities

TL;DR

This paper demonstrates that Fix and Pair techniques, combined with matching initial conditions, effectively reduce variance in galaxy clustering simulations with primordial non-Gaussianities, enabling more precise testing of cosmological models.

Contribution

It introduces a validated method to reduce variance in simulations with primordial non-Gaussianities using Fix, Pair, and Match techniques, improving model testing accuracy.

Findings

Variance in f_NL estimates is significantly reduced using Fix and Pair techniques.

Matching initial conditions further enhances correlation and reduces uncertainty.

Combined methods effectively increase simulation volume without additional computational cost.

Abstract

The Fix and Pair techniques were designed to generate simulations with reduced variance in the 2-point statistics by modifying the Initial Conditions (ICs). In this paper we show that this technique is also valid when the initial conditions have local Primordial non-Gaussianities (PNG), parametrised by $f_{\rm NL}$, without biasing the 2-point statistics but reducing significantly their variance. We show how to quantitatively use these techniques to test the accuracy of galaxy/halo clustering models down to a much reduced uncertainty and we apply them to test the standard model for halo clustering in the presence of PNG. Additionally, we show that by Matching the stochastic part of the ICs for two different cosmologies (Gaussian and non-Gaussian) we obtain a large correlation between the (2-point) statistics that can explicitly be used to further reduce the uncertainty of the model testing. For our reference analysis ($f_{\rm NL}=100$, $V=1 [h^{-1}{\rm Gpc}]^3$, $n= 2.5\times 10^{-4}[h^{-1}{\rm Mpc}]^{-3}$, $b=2.32$), we obtain an uncertainty of $\sigma(f_{\rm NL})=60$ with a standard simulation, whereas using Fixed [Fixed-Paired] initial conditions it reduces to $\sigma(f_{\rm NL})=12$ [$\sigma(f_{\rm NL})=12$]. When also Matching the ICs we obtain $\sigma (f_{\rm NL})=18$ for the standard case, and $\sigma (f_{\rm NL})=8$ [$\sigma (f_{\rm NL})=7$] for Fixed [Fixed-Paired]. The combination of the Fix, Pair and Match techniques can be used in the context of PNG to create simulations with an effective volume incremented by a factor $\sim 70$ at given computational resources.