Cluster-Void Degeneracy Breaking: Modified Gravity in the Balance

TL;DR

This paper proposes combining galaxy cluster and void abundances to significantly improve constraints on modified gravity and dark energy models, especially with future surveys like Euclid and 4MOST.

Contribution

It introduces a novel method of combining void and cluster data to enhance constraints on deviations from General Relativity and the $ m extLambda$CDM model.

Findings

Combining void and cluster abundances can improve the Figure of Merit by a factor of 20.

Future surveys could achieve a Figure of Merit 600 times better than current data.

The method effectively constrains the growth index parameters in modified gravity models.

Abstract

Combining galaxy cluster and void abundances is a novel, powerful way to constrain deviations from General Relativity and the $\Lambda$CDM model. For a flat $w$CDM model with growth of large-scale structure parameterized by the redshift-dependent growth index $\gamma(z) = \gamma_0 + \gamma_1 z/(1+z)$ of linear matter perturbations, combining void and cluster abundances in future surveys with Euclid and the 4-metre Multi-Object Spectroscopic Telescope (4MOST) could improve the Figure of Merit for ($w, \gamma_0, \gamma_1$) by a factor of 20 compared to individual abundances. In an ideal case, improvement on current cosmological data is a Figure of Merit factor $600$ or more.