Classical electrodynamics and spin-torsion coupling effects

TL;DR

This paper explores how axial torsion in Poincaré gauge gravity interacts with electromagnetic fields, leading to polarization rotation effects in electromagnetic waves under external fields.

Contribution

It introduces a novel analysis of spin-torsion coupling in a quadratic Poincaré gauge theory, linking electromagnetic helicity and spin densities to torsion sources.

Findings

Identification of magnetic helicity and spin density as torsion sources

Demonstration of polarization rotation (dichroism) effect

Analysis of electromagnetic wave propagation in torsion-influenced spacetime

Abstract

We study the Poincar\'e gauge theory of gravity with the most general Lagrangian quadratic in curvature and torsion, focusing on the possible interaction of the axial torsion with the electromagnetic field. From the analysis of the closed system of field equations, we identify the magnetic helicity density and the spin density of the electromagnetic field as the components of the source for the torsion field. We consider the propagation of a linearly polarized plane electromagnetic wave and demonstrate the ``dichroism'' or the polarization rotation effect under the action of external electric and magnetic fields orthogonal to the direction of wave propagation.