Testing the imprint of nonstandard cosmologies on void profiles using Monte Carlo random walks

Abstract

Using a Monte Carlo random walks of a log-normal distribution, we show how to qualitatively study void properties for non-standard cosmologies. We apply this method to an f (R) modified gravity model and recover the N-body simulation results of [1] for the void profiles and their deviation from GR. This method can potentially be extended to study other properties of the large scale structures such as the abundance of voids or overdense environments. We also introduce a new way to identify voids in the cosmic web, using only a few measurements of the density fluctuations around random positions. This algorithm allows to select voids with specific profiles and radii. As a consequence, we can target classes of voids with higher differences between f (R) and standard gravity void profiles. Finally we apply our void criteria to galaxy mock catalogues and discuss how the flexibility of our void finder can be used to reduce systematics errors when probing the growth rate in the galaxy-void correlation function.

New constraints on the linear growth rate using cosmic voids in the SDSS DR12 datasets

“…• Our void catalogues are completely independent and based on different criteria (density criteria [1] vs. watershed transform [41]). While the peak of the void size distribution is relatively similar in both studies, we have better statistics on the number of voids in the LOWZ sample.…”

“…First, certain models of modified gravity, such as f (R) [25], rely on the the chameleon screening mechanism [29] which suppresses the 5th force in high density regions, while in under-dense regions the total gravitational force is enhanced (due to the presence of the 5th force), resulting in specific imprints on void abundance and density profiles around underdense regions (e.g. [1,3,6,11,15,45]). These theories would naturally lead to an environmentally-dependent growth rate.…”

Modeling the environmental dependence of the growth rate of cosmic structure

“…To do this, we analyse the growth rate using numerical simulations in and around overdense and underdense regions and show how it can be predicted as a function of local density and for a given cosmology. This prediction relies on log-normal Monte Carlo Random Walks, a method introduced in [13]. We find that our model is successful in tracking the evolution of the growth rate at different local density environments.…”

“…environement) in the simulations, where R is the radius of the region. We follow the method presented in [13] to identify low density regions, i.e. voids.…”

“…This algorithm imposes density thresholds at the radius of our choice, therefore allowing flexibility to represent a large variety of void profiles. Here we choose R = 20h −1 Mpc and the same criteria for the voids as the ones used in [13]. This fiducial size is statistically motivated to obtain enough non-overlapping voids.…”