Cluster-Void Degeneracy Breaking: Dark Energy, Planck and the Largest Cluster & Void

TL;DR

This paper demonstrates that combining galaxy cluster and void abundances can effectively break parameter degeneracies, providing independent constraints on dark energy and cosmological parameters using extreme-value statistics.

Contribution

It introduces a novel approach using voids and clusters to constrain cosmology, achieving the first such constraints with extreme-value statistics on the largest objects.

Findings

Constrained $ ext{Ω}_ ext{m}$ and $ ext{σ}_8$ using voids and clusters.

Detected dark energy with just two objects, consistent with Planck.

Showed complementarity of cluster-void studies for testing gravity.

Abstract

Combining galaxy cluster and void abundances breaks the degeneracy between mean matter density $\Omega_{\rm m}$ and power spectrum normalization $\sigma_8$. In a first for voids, we constrain $\Omega_{\rm m} = 0.21 \pm 0.10$ and $\sigma_8 = 0.95 \pm 0.21$ for a flat $\Lambda$CDM universe, using extreme-value statistics on the claimed largest cluster and void. The Planck-consistent results detect dark energy with two objects, independently of other dark energy probes. Cluster-void studies also offer complementarity in scale, density, and non-linearity - of particular interest for testing modified-gravity models.