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

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

2009-12-12

arxiv.org/abs/0912.2461v3

Astronomy and Astrophysics

Astrophysics

General Relativity and Quantum Cosmology

Departamento de Fisica Teorica-IF-UERJ-Rio-RJ-Brasil

Scientific paper

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)].

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