An angular rainbow of light from curved spacetime

TL;DR

This paper explores beyond geometrical optics to show how massless polarized particles interact with curved spacetime, leading to frequency-dependent polarization effects such as angular dispersion in gravitational fields.

Contribution

It introduces a class of non-minimal interactions between polarized particles and gravity, demonstrating a curvature-dependent Faraday effect beyond standard optics approximations.

Findings

Frequency-dependent Faraday effect observed in Schwarzschild spacetime.

Angular dispersion of polarization planes for different frequencies.

Non-minimal interactions cause polarization effects in curved spacetime.

Abstract

We try to go beyond the geometrical optics approximation, by showing that a massless polarized particle allows a wide class of non minimal interactions with an arbitrary gravitational field. One specific example of a curvature-dependent interaction is presented, that results in a frequency-dependent Faraday effect. Even in a Schwarzschild spacetime, this leads to the angular dispersion of polarization planes for a linearly-polarized beam of waves with different frequencies, propagating along the same ray.