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