A Simultaneous Constraint on the Amplitude and Gaussianity of Mass Fluctuations in the Universe

TL;DR

This paper combines observations of galaxy clusters and their correlations to tightly constrain the amplitude and Gaussianity of primordial mass fluctuations, ruling out Gaussianity in certain cosmological models.

Contribution

It introduces a method to simultaneously constrain the amplitude and non-Gaussianity of primordial fluctuations using multiple observational constraints.

Findings

For a flat Omega_m=1 universe, sigma_8=0.49 with uncertainties.

Gaussian primordial fluctuations are consistent with data in some models.

Gaussianity is ruled out in low matter density models.

Abstract

We consider constraints on the amplitude of mass fluctuations in the universe, sigma_8, derived from two simple observations: the present number density of clusters and the amplitude of their correlation function. Allowing for the possibility that the primordial fluctuations are non-gaussian introduces a degeneracy in the value of sigma_8 preferred by each of these constraints. However, when the constraints are taken together this degeneracy is broken, yielding a precise determination of sigma_8 and the degree of non-gaussianity for a given background cosmology. For a flat, Omega_m=1 universe with a power spectrum parameterized by a CDM shape parameter Gamma=0.2, we find that the perturbations are consistent with a gaussian distribution with sigma_8=0.49(+0.08-0.07) (95% limits). For some popular choices of background model, including the favored low matter density models, the hypothesis that the primordial fluctuations are gaussian is ruled out with a high degree of confidence.