Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation

Abstract

In this letter we provide a simple explanation of the recent finding of anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston. We consider, as a possible origin of such effect, the effective coupling between EM fields and some tiny background torsion field. The coupling is obtained after integrating out charged fermions, it is gauge-invariant and does not require the introduction of any new physics.