A Simultaneous Constraint on the Amplitude and Gaussianity of Mass Fluctuations in the Universe
Abstract
We consider constraints on the amplitude of mass fluctuations in the universe, sigma8, 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 sigma8 preferred by each of these constraints. However, when the constraints are taken together this degeneracy is broken, yielding a precise determination of sigma8 and the degree of non-gaussianity for a given background cosmology. For a flat, Omegam=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 sigma8=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.
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