Probing gravity with redshift-space distortions: effects of tracer bias and sample selection

TL;DR

This study uses large cosmological simulations to analyze redshift-space distortions and clustering ratios, aiming to detect deviations from general relativity caused by modified gravity models, while addressing tracer bias effects.

Contribution

It introduces new bias-independent clustering statistics and an estimator for the $eta$ parameter, enhancing the ability to distinguish modified gravity models from GR.

Findings

Noticeable MG signals in 2PCF monopole and quadrupole moments.

Clustering ratios show deviations up to 10\% between MG and GR models.

Optimal tracer selection depends on the specific statistic and gravity model.

Abstract

We investigate clustering properties of dark matter halos and galaxies to search for optimal statistics and scales where possible departures from general relativity (GR) could be found. We use large N-body cosmological simulations to perform measurements based on the two-point correlation function (2PCF) in GR and in selected modified gravity (MG) structure formation scenarios. As a test-bed, we employ two popular beyond-GR models: $f(R)$ gravity and the normal branch of the Dvali-Gabadadze-Porrati (nDGP) braneworld. We study a range of simulated halo and galaxy populations and reveal a noticeable MG signal in the monopole and quadrupole moments of the redshift-space 2PCF, and in the so-called clustering wedges. However, once expressed in terms of the linear distortion parameter, $\beta$, the statistical significance of these signals largely diminishes due to a strong degeneracy between MG-enhanced clustering and modified tracer bias. To circumvent this, we consider statistics less dependent on the bias: relative clustering ratios. We generalize the monopole ratio proposed in earlier work to multipole moments and clustering wedges, and introduce a new estimator of the $\beta$ parameter. The clustering ratios we extract foster noticeable differences between MG and GR models, reaching a maximum deviation of 10\% at 2$\sigma$ significance for specific variants of $f(R)$ and nDGP. We show that such departures could be measured for $\beta$ if non-linear effects at intermediate scales are correctly modeled. Our study indicates that the clustering ratios give great promise to search for signatures of MG in the large-scale structure. We also find that the selection of an optimal tracer sample depends on a particular statistics and gravity model to be considered.