Decoupling between torsion and magnetic fields in bouncing cosmology and galactic dynamo seeds

TL;DR

This paper explores how torsion in spacetime affects magnetic field evolution in bouncing cosmology, showing that magnetic fields can grow rapidly and decouple from torsion, potentially seeding galactic dynamos.

Contribution

It generalizes previous models by including torsion effects and demonstrates a mechanism for rapid magnetic field amplification during contraction.

Findings

Magnetic field grows as B ~ a^{-5.5} during contraction.

Torsion field decays as K ~ a^{2/3}.

Decoupling occurs rapidly, enabling seed magnetic fields for galaxies.

Abstract

Recently Salim et al [JCAP (2007)], have shown that galactic dynamo seeds can be possibly attainable in bouncing cosmological models with QED Lagrangeans. In this paper we generalise their result by include torsion of spacetime in bouncing cosmology. It is shown that by considering a semi-minimal photon-torsion coupling and a Lagrangean of the type $RF^{2}$ it is possible to find a fast decoupling between magnetic and torsion fields in the contracting phases of the universe. Besides torsion field decays as $K\sim{a^{2/3}}$ while the magnetic field grows as $B\sim{a^{-5.5}}$ thus explaining the fast decoupling between the two fields. It is expected that at some point of the contracting phase the amplification of the magnetic field may give rise to a enough strong magnetic field to seed a galactic dynamo.