Magnetohydrodynamic processes in strongly magnetized young neutron stars

We examine the early evolution of a neutron star with a very strong magneti c field (B greater than or equal to 4 x 10(13) G) that occupies a significa nt fraction of the core volume. The electrical conductivity of the core mat ter is a strong function of the magnetic field, therefore the evolution of magnetized neutron stars (magnetars) may well be different from that of ord inary radiopulsars. We consider magnetohydrodynamic processes in the core f or two possible models of nuclear matter, with normal and superfluid neutro ns. In the case of the normal matter, an enhancement of the resistivity per pendicular to the magnetic field can result in rapid field decay during the early evolutionary stage. If neutrons are in the superfluid state, we find that the Hall effect can lead to oscillatory behaviour of the magnetic fie ld. This oscillatory behaviour is caused by the generation of large-scale h elicoid modes resulting from non-linear coupling between the different fiel d components.