The Search for Primordial Non-Gaussianity in the Large-Scale Structure of the Universe

Abstract

Primordial non-Gaussianity is one of the most promising means at our disposal for probing the physics of Inflation. Recently, the Planck Collaboration has used observations of the cosmic microwave background to determine the level of non-Gaussianity to an unprecedented accuracy of flocal NL = 2:7 5:8. However, this result still leaves the door open to many theories of Inflation, and obtaining tighter constraints through other observations would provide valuable information about the physics of the early Universe. We study the impact of primordial non-Gaussianity on large-scale structure and demonstrate how these effects can be used to constrain the level of non-Gaussianity. The observable effects we consider include the influence of non-Gaussianity on the abundance of galaxies and galaxy clusters, on the large-scale clustering of dark matter halos, and on the process of reionization. We roughly calculate the accuracy with which the first two of these can be used to constrain the level of non-Gaussianity, obtaining estimated constraints of (fNL) 12 and (fNL) 4, respectively. The latter constraint would be a slight improvement on the Planck results. We then compare our results to recent estimates of constraints using the effects of non- Gaussianity on reionization. We find that while the expected reionization constraints are tighter, they rely on technology and observations that are not yet available. We expect that an accuracy of (fNL) 4 can be reached using existing observations of a population of high-redshift “sub-millimeter galaxies.”