Non-Gaussianity in Cosmology: from Inflation to the CMB

TL;DR

This thesis reviews the theoretical formalism and observational methods for studying non-Gaussianities in inflationary cosmology, focusing on the bispectrum and its analysis in CMB data, especially from Planck.

Contribution

It introduces the long-wavelength formalism for calculating non-Gaussianities in multi-field inflation and the binned bispectrum estimator for analyzing CMB data.

Findings

The formalism enables computation of non-Gaussianities in complex inflation models.

The binned bispectrum estimator effectively constrains primordial non-Gaussianity from Planck data.

The work provides the best current limits on primordial non-Gaussianity.

Abstract

The non-Gaussianity of inflationary perturbations, as encoded in the bispectrum (or 3-point correlator), has become an important additional way of distinguishing between inflation models, going beyond the linear Gaussian perturbation quantities of the power spectrum. This habilitation thesis provides a review of my work on both the theoretical and the observational aspects of these non-Gaussianities. In the first part a formalism is described, called the long-wavelength formalism, that provides a way to compute the non-Gaussianities in multiple-field inflation. Applications of this formalism to various classes of models, as well as its extensions, are also treated. In the second part an estimator is described, called the binned bispectrum estimator, that allows the extraction of information about non-Gaussianities from data of the cosmic microwave background radiation (CMB). It was in particular one of the three estimators applied to the data of the Planck satellite to provide the currently best constraints on primordial non-Gaussianity. Various extensions of the estimator and results obtained are also discussed.