Validating galaxy clustering models with fixed and paired and matched-ICs simulations: application to primordial non-Gaussianities

Abstract

ABSTRACT The Fix and Pair techniques were designed to generate simulations with reduced variance in the two-point statistics by modifying the initial conditions (ICs). In this paper we show that this technique is also valid when the ICs have local primordial non-Gaussianities (PNG), parametrized by fNL, without biasing the two-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 (two-point) statistics that can explicitly be used to further reduce the uncertainty of the model testing. For our reference analysis (fNL = 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 σ(fNL) = 60 with a standard simulation, whereas using Fixed [Fixed-Paired] ICs it reduces to σ(fNL) = 12 [σ(fNL) = 12]. When also Matching the ICs we obtain σ(fNL) = 18 for the standard case, and σ(fNL) = 8 [σ(fNL) = 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 ∼70 at given computational resources.