Mean-field cosmological dynamo curvature vs turbulence spectrum in Riemannian space

TL;DR

This paper develops a mean-field dynamo model on a Riemannian cosmological background, coupling turbulence and curvature, and finds that the curvature turbulence spectrum resembles the Kolmogorov spectrum, with implications for cosmic magnetic fields.

Contribution

It introduces a mean-field dynamo framework incorporating Ricci curvature effects in cosmology, extending previous models to include turbulence spectrum analysis.

Findings

The dynamo growth rate in a G"odel universe is proportional to vorticity and turbulent diffusivity.

The magnetic field during nucleosynthesis could reach approximately 10^{10} G.

The Ricci scalar turbulence spectrum aligns with the Kolmogorov spectrum.

Abstract

Previous attempts for building a cosmic dynamo including preheating in inflationary universes [Bassett et al Phys Rev (2001)] has not included mean field dynamos. Here, a mean field dynamo in cosmic scales on a Riemannian spatial cosmological section background, is set up. When magnetic fields and flow velocities are parallel propagated along the Riemannian space dynamo action is obtained. Turbulent diffusivity ${\beta}$ is coupled with the Ricci magnetic curvature, as in Marklund and Clarkson [MNRAS (2005)], GR-MHD dynamo equation. Mean electric field possesses an extra term due to Ricci tensor coupling with magnetic vector potential in Ohm's law. Goedel universe induces a mean field dynamo growth rate ${\gamma}=2{\omega}^{2}{\beta}$. In this frame kinetic helicity vanishes. By considering a universe vorticity, ${\omega}\approx{10^{-16}s^{-1}}$ for galactic dynamos, thus ${\gamma}=2.10^{-32}{\beta}$, and since ${\beta}\approx{10^{26}cm^{2}s^{-1}}$, the growth rate ${\gamma}\approx{10^{-6}s^{-1}}$. In non-comoving the magnetic field is expressed as $B\approx{\sqrt{\frac{2{\beta}}{\gamma}}{\times}10^{-6}G}\approx{10^{10}G}$ a magnetic field found in the nucleosynthesis era. The Ricci scalar turbulence spectrum of the cosmic dynamos is computed from the GR-MHD dynamo equation. By analyzing the Fourier modes of the Ricci scalar, one shows that the energy spectrum of the curvature turbulent dynamo is similar to the Kolmogorov spectrum. Similar enhancements of turbulence in Friedmann cosmology have been obtained by Brandenburg et al [Phys Rev D (1997)].