Revealing modified gravity signals in matter and halo hierarchical clustering

Abstract

We use a set of N-body simulations employing a modified gravity (MG) model with Vainshtein screening to study matter and halo hierarchical clustering. As test-case scenarios we consider two normal branch Dvali-Gabadadze-Porrati (nDGP) gravity models with mild and strong growth rate enhancement. We study higher-order correlation functions ξn(R) up to n = 9 and associated hierarchical amplitudes Sn(R) ≡ ξn(R)/σ(R) 2n−2 . We find that the matter PDFs are strongly affected by the fifth-force on scales up to 50h −1 Mpc, and the deviations from GR are maximised at z = 0. For reduced cumulants Sn, we find that at small scales R ≤ 10h −1 Mpc the MG is characterised by lower values, with the deviation growing from 7% in the reduced skewness up to even 40% in S5. To study the halo clustering we use a simple abundance matching and divide haloes into thee fixed number density samples. The halo two-point functions are weakly affected, with a relative boost of the order of a few percent appearing only at the smallest pair separations (r ≤ 5h −1 Mpc). In contrast, we find a strong MG signal in Sn(R)'s, which are enhanced compared to GR. The strong model exhibits a > 3σ level signal at various scales for all halo samples and in all cumulants. In this context, we find that the reduced kurtosis to be an especially promising cosmological probe of MG. Even the mild nDGP model leaves a 3σ imprint at small scales R ≤ 3h −1 Mpc, while the stronger model deviates from a GR-signature at nearly all scales with a significance of > 5σ. Since the signal is persistent in all halo samples and over a range of scales, we advocate that the reduced kurtosis estimated from galaxy catalogues can potentially constitute a strong MG-model discriminatory as well as GR self-consistency test.

Testing general relativity in cosmology

“…nDGP are used as benchmark to develop and test frameworks for MG studies as in for example the nonlinear regime, e.g., Hellwing et al. ( 2017 ) and Bose et al. ( 2018 ).…”

An accurate perturbative approach to redshift space clustering of biased tracers in modified gravity

“…In this section, we briefly introduce the N-body simulations we will use to assess the performance of our analytical model, which is a crucial step for our analysis. The first set of simulations, that we will refer to from now on as Group I simulations, are the Extended LEnsing PHysics using ANalaytic ray Tracing (ELEPHANT) simulations [94], that were performed with two modified versions of the GR code (RAMSES): the ECOSMOG module [95,96] produced snapshots for the F6, F5 and F4 cases at a cosmological redshift of z = 0.5, while ECOSMOG-V [97][98][99] was used to produce the nDGP N1 and N5 realizations, also at z = 0.5. 1024 3 dark matter particles were evolved, in a simulation box with a side L box = 1024M pc/h and a cosmology specified by the following parameters:…”

“…We wish to thank Baojiu Li for kindly providing the ELEPHANT simulations, on behalf of [94] and for numerous discussions on available simulations. We would also like to thank Wojciech Hellwing for kindly making available the nDGP simulations, on behalf of [99], as well as Christian Arnold, together with the other authors of [101], for kindly providing their Lightcone simulations. We are also grateful to Martin White for providing valuable insights on perturbation theory and available simulations and also to Uros Seljak, Emanuele Castorina and Steven Chen for useful discussions.…”

The matter density PDF for modified gravity and dark energy with Large Deviations Theory

“…The probability distribution function (hereafter PDF) of the threedimensional matter density field smoothed on a given scale is one of the simplest non-Gaussian statistics, and accurate predictions allow us to extract additional cosmological information (Uhlemann et al 2020). Modified gravity and evolving dark energy leave distinctive imprints on the skewness, kurtosis and higher cumulants of the PDF, which have been observed in 𝑁-body simulations (Li et al 2012b;Hellwing et al 2013Hellwing et al , 2017Shin et al 2017). Thus far, theoretical predictions of the PDF for modified gravity have required either sophisticated and time-consuming approaches for the spherical collapse (Brax & Valageas 2012) or computationally costly simulations (Li et al 2012b;Hellwing et al 2013Hellwing et al , 2017.…”