Maxwell equations in a curved spacetime: Spin optics approximation

TL;DR

This paper introduces the spin optics approximation, a covariant method to analyze high-frequency electromagnetic wave propagation in curved spacetime, accounting for helicity-dependent corrections to polarization ray trajectories.

Contribution

It presents a novel covariant approximation method that incorporates helicity effects into electromagnetic wave propagation in arbitrary gravitational fields.

Findings

Polarized light rays are null but not geodesic.

The spin optics approximation is applicable in arbitrary time-dependent gravitational fields.

Null frames are constructed for non-geodesic null rays.

Abstract

We study propagation of high-frequency electromagnetic waves in a curved spacetime. We demonstrate how a modification of the standard geometric optics allows one to include the helicity dependent corrections into the equations of motion of circularly polarized beams of radiation. As a result, polarized light rays are still null but not geodesic curves. To achieve these results we construct null frames associated with a set of (non-geodesic) null rays and use these frames for description of the high-frequency wave propagation. We call this approach spin optics approximation. It is completely covariant and it can be used in an arbitrary time-dependent gravitational field.