paper

On inverse Cascades and Primordial Magnetic Fields

arXiv:astro-ph/9610154 · doi:10.1016/S0370-2693(97)00235-9

Abstract

We consider primordial spectra with simple power behaviours and show that in the Navier-Stokes and magnetohydrodynamics equations without forcing, there exists systems in three dimensions with a subsequent inverse cascade, transferring energy from small to large spatial scales. This can have consequences in astrophysics for the evolution of density fluctuations, for primordial magnetic fields, and for the effect of diffusion. In general, if the initial spectrum is k^{alpha}, then in the ``inertial'' range, for alpha >-3 there is an inverse cascade, whereas for alpha<-3 there is a forward cascade.

7 pages, LaTex. The title has been changed, and a new introduction has been included. No changes in any of the results. This paper has been accepted for publication in Physics Letters B

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