Vorticity from isocurvature in the early universe

TL;DR

This paper explores how vorticity can be generated in the early universe from scalar perturbations, specifically through entropy gradients, which could help distinguish between different inflationary models.

Contribution

It demonstrates that second-order cosmological perturbations can produce vorticity from isocurvature modes, extending classical fluid dynamics concepts to cosmology.

Findings

Vorticity is sourced by energy density and entropy gradient coupling.

Induced vorticity may serve as a discriminator between inflationary models.

Vorticity generation from scalar perturbations is significant at second order.

Abstract

Vorticity is ubiquitous in nature however, to date, studies of vorticity in cosmology and the early universe have been quite rare. In this paper, based on a talk in session CM1 of the 13th Marcel Grossmann Meeting, we consider vorticity generation from scalar cosmological perturbations of a perfect fluid system. We show that, at second order in perturbation theory, vorticity is sourced by a coupling between energy density and entropy gradients, thus extending a well-known feature of classical fluid dynamics to a relativistic cosmological framework. This induced vorticity, sourced by isocurvature perturbations, may prove useful in the future as an additional discriminator between inflationary models.