Spin optics for gravitational waves

TL;DR

This paper develops a spin optics framework for gravitational waves, extending geometric optics to include helicity-dependent corrections, and adapts electromagnetic wave techniques to gravitational waves considering helicity differences.

Contribution

It introduces the concept of spin optics for gravitational waves, incorporating helicity-dependent modifications to the geometric optics expansion on curved backgrounds.

Findings

Derived the subleading order geometric optics expansion for gravitational waves.

Demonstrated the application of electromagnetic wave propagation techniques to gravitational waves.

Accounted for helicity differences between photons and gravitons in the analysis.

Abstract

We present the geometric optics expansion for circularly polarized gravitational waves on a curved spacetime background, to subleading order. We call spin optics to the subleading order geometric optics expansion, which involves modifying the standard eikonal function by including a specially chosen helicity-dependent correction. We show that the techniques developed for the propagation of electromagnetic waves can also be applied to gravitational waves in the limit of spin optics. However, one needs to account for the difference in the photon and graviton helicity, which we do here.