Astrophysical chiral dynamos and strain-torsioned Weyl materials

Abstract

Our goal in this paper is two-fold: First we show that in the absence of four-fermion interactions, from Einstein–Cartan–Maxwell (ECM) anisotropy cosmology, one may derive instabilities in chiral dynamo equations from magnetic perturbations. They are obtained from a model, where the spinning-fluid does not couple directly to the Einstein–Maxwell model. Instead spin fluid enter into the evolution equation of density perturbations. Chiral dynamo equation is obtained from magnetic perturbations in the particular case where the perturbations in the chiral magnetized plasma can be neglected in second order of perturbations. The vanishing of the Nieh–Yan (NY) topological density in this Bianchi type-I model is also investigated. In the second example, use of the magnetic and torsion perturbations are given by the technique of encoding the magnetic perturbations in the metric constrained by teleparallelism. We consider non-uniform chiral chemical potential in the chiral flipping equation in order to obtain the magnetic field dynamo amplification. Dynamo effects are obtained from current perturbations expressed in terms of chiral chemical potential when number density of left-handed chiral particles is approximately zero. The damping found in magnetic field by the end of inflation, may help to explain why so weak galactic dynamo seeds are found at present universe. Furthermore, damping depends upon the strain–torsion relation of the Weyl topological materials. Though in general, torsion does not couple to electromagnetic fields, it influences the magnetic field through strain–torsion pseudo-magnetic potential.