Magnetised cosmological perturbations in the post-recombination era
  We study inhomogeneous magnetised cosmologies through the post-recombination
era in the framework of Newtonian gravity and the ideal-magnetohydrodynamic
limit. The nonlinear kinematic and dynamic equations are derived and linearised
around the Newtonian counterpart of the Einstein-de Sitter universe. This
allows for a direct comparison with the earlier relativistic treatments of the
issue. Focusing on the evolution of linear density perturbations, we provide
new analytic solutions which include the effects of the magnetic pressure as
well as those of the field's tension. We confirm that the pressure of field
inhibits the growth of density distortions and can induce a purely magnetic
Jeans length. On scales larger than the aforementioned characteristic length
the inhomogeneities grow, though slower than in non-magnetised universes.
Wavelengths smaller than the magnetic Jeans length typically oscillate with
decreasing amplitude. We also identify a narrow range of scales, just below the
Jeans length, where the perturbations exhibit a slower power-law decay. In all
cases, the effect of the field is proportional to its strength and increases as
we move to progressively smaller lengths.
