The future of cosmology and the role of non-linear perturbations

TL;DR

This paper discusses the importance of non-linear cosmological perturbation theory, especially second-order effects like vorticity, for advancing our understanding of the universe and testing cosmological models.

Contribution

It highlights the significance of second-order perturbations, such as vorticity, as signatures that extend beyond linear theory in cosmology.

Findings

Vorticity generation at second order is a key signature.

Non-linear effects like gravitational waves and non-Gaussianities are crucial.

Non-linear perturbation theory enhances testing of cosmological models.

Abstract

Cosmological perturbation theory is a key tool to study the universe. The linear or first order theory is well understood, however, developing and applying the theory beyond linear order is at the cutting edge of current research in theoretical cosmology. In this article, I will describe some signatures of non-linear perturbation theory that do not exist at linear order, focusing on vorticity generation at second order. In doing so, we discuss why this, among other features such as induced gravitational waves and non-Gaussianities, shows that cosmological perturbation theory is crucial for testing models of the universe.