Cosmic strings and their induced non-Gaussianities in the cosmic microwave background

TL;DR

Cosmic strings can produce distinctive non-Gaussian features in the CMB, offering a unique probe of early universe physics beyond primordial inflationary fluctuations.

Contribution

This paper reviews the cosmological effects of cosmic strings and analyzes their specific non-Gaussian signatures in the CMB, highlighting their distinguishability from primordial non-Gaussianities.

Findings

Cosmic strings induce unique non-Gaussian patterns in the CMB.

String signatures differ significantly from primordial non-Gaussianities.

Cosmic strings could be the main source of non-Gaussianities despite small power spectrum contributions.

Abstract

Motivated by the fact that cosmological perturbations of inflationary quantum origin were born Gaussian, the search for non-Gaussianities in the cosmic microwave background (CMB) anisotropies is considered as the privileged probe of non-linear physics in the early universe. Cosmic strings are active sources of gravitational perturbations and incessantly produce non-Gaussian distortions in the CMB. Even if, on the currently observed angular scales, they can only contribute a small fraction of the CMB angular power spectrum, cosmic strings could actually be the main source of its non-Gaussianities. In this article, after having reviewed the basic cosmological properties of a string network, we present the signatures Nambu-Goto cosmic strings would induce in various observables ranging from the one-point function of the temperature anisotropies to the bispectrum and trispectrum. It is shown that string imprints are significantly different than those expected from the primordial type of non-Gaussianity and could therefore be easily distinguished.