Effects of Scale-Dependent Non-Gaussianity on Cosmological Structures

TL;DR

This paper investigates how scale-dependent primordial non-Gaussianity influences the formation of cosmological structures, such as galaxy clusters, and forecasts how upcoming data can constrain these models, especially in the context of brane inflation.

Contribution

It introduces a simple model for scale-dependent non-Gaussianity and analyzes its effects on cluster counts and galaxy bispectrum, providing forecasts for future observational constraints.

Findings

Scale-dependent non-Gaussianity affects cluster number counts.

Forecasts show potential to constrain models with upcoming data.

Implications for brane inflation models are discussed.

Abstract

The detection of primordial non-Gaussianity could provide a powerful means to test various inflationary scenarios. Although scale-invariant non-Gaussianity (often described by the $f_{NL}$ formalism) is currently best constrained by the CMB, single-field models with changing sound speed can have strongly scale-dependent non-Gaussianity. Such models could evade the CMB constraints but still have important effects at scales responsible for the formation of cosmological objects such as clusters and galaxies. We compute the effect of scale-dependent primordial non-Gaussianity on cluster number counts as a function of redshift, using a simple ansatz to model scale-dependent features. We forecast constraints on these models achievable with forthcoming data sets. We also examine consequences for the galaxy bispectrum. Our results are relevant for the Dirac-Born-Infeld model of brane inflation, where the scale-dependence of the non-Gaussianity is directly related to the geometry of the extra dimensions.