The turbulent chiral-magnetic cascade in the early universe

TL;DR

This paper investigates how chiral magnetic effects in early universe plasmas lead to turbulence and specific magnetic energy spectra, with implications for cosmic magnetic field evolution.

Contribution

It demonstrates, through simulations and dimensional analysis, that chiral magnetic effects induce turbulence and a characteristic magnetic spectrum in the early universe.

Findings

Emergence of a k^{-2} magnetic energy spectrum

Transfer of chirality into magnetic helicity

Conservation of total chirality in the system

Abstract

The presence of asymmetry between fermions of opposite handedness in plasmas of relativistic particles can lead to exponential growth of a helical magnetic field via a small-scale chiral dynamo instability known as the chiral magnetic effect. Here, we show, using dimensional arguments and numerical simulations, that this process produces through the Lorentz force chiral magnetically driven turbulence. A k^{-2} magnetic energy spectrum emerges via inverse transfer over a certain range of wavenumbers k. The total chirality (magnetic helicity plus normalized chiral chemical potential) is conserved in this system. Therefore, as the helical magnetic field grows, most of the total chirality gets transferred into magnetic helicity until the chiral magnetic effect terminates. Quantitative results for height, slope, and extent of the spectrum are obtained. Consequences of this effect for cosmic magnetic fields are discussed.