# Birefringence induced by pp-wave modes in an electromagnetically active dynamic aether

## TL;DR

This paper investigates how pp-wave modes in a dynamic aether can induce birefringence in electromagnetic waves, revealing polarization-dependent phase velocity differences due to gravitational effects in Einstein-Maxwell-aether theory.

## Contribution

It introduces a model of birefringence caused by pp-wave modes in a dynamic aether, considering susceptibility tensors linear in the aether velocity derivatives, and analyzes electromagnetic responses in this context.

## Key findings

- Electromagnetic waves exhibit birefringence in the presence of pp-wave modes.
- Phase velocities of orthogonal polarizations differ due to gravitationally induced degeneracy removal.
- Anomalies in electromagnetic response are found for longitudinal and transversal configurations.

## Abstract

In the framework of the Einstein-Maxwell-aether theory we study the birefringence effect, which can occur in the pp-wave symmetric dynamic aether. The dynamic aether is considered to be latently birefringent quasi-medium, which displays this hidden property if and only if the aether motion is non-uniform, i.e., when the aether flow is characterized by the non-vanishing expansion, shear, vorticity or acceleration. In accordance with the dynamo-optical scheme of description of the interaction between electromagnetic waves and the dynamic aether, we shall model the susceptibility tensors by the terms linear in the covariant derivative of the aether velocity four-vector. When the pp-wave modes appear in the dynamic aether, we deal with a gravitationally induced degeneracy removal with respect to hidden susceptibility parameters. As a consequence, the phase velocities of electromagnetic waves possessing orthogonal polarizations do not coincide, thus displaying the birefringence effect. Two electromagnetic field configurations are studied in detail: longitudinal and transversal with respect to the aether pp-wave front. For both cases the solutions are found, which reveal anomalies in the electromagnetic response on the action of the pp-wave aether mode.