On spin optics for gravitational waves lensed by a rotating object

TL;DR

This paper investigates how the spin of gravitons affects gravitational wave lensing by rotating objects, revealing helicity-dependent effects that could inform future low-frequency gravitational wave observations.

Contribution

It introduces a spin optics framework for analyzing gravitational wave lensing by rotating bodies, highlighting helicity-dependent phase and polarization effects.

Findings

Helicity-dependent splitting of gravitational wave trajectories.

Analytical expressions for phase and magnification corrections.

Enhanced effects for longer wavelengths, useful for probing rotation.

Abstract

We study gravitational lensing of gravitational waves taking into account the spin of a graviton coupled with a dragged spacetime made by a rotating object. We decompose the phase of gravitational waves into helicity-dependent and independent components with spin optics, analyzing waves whose wavelengths are shorter than the curvature radius of a lens object. We analytically confirm that the trajectory of gravitational waves splits depending on the helicity, generating additional time delay and elliptical polarization onto the helicity-independent part. We exemplify monotonic gravitational waves lensed by a Kerr black hole and derive the analytical expressions of corrections in phase and magnification. The corrections are enhanced for longer wavelengths, potentially providing a novel probe of rotational properties of lens objects in low-frequency gravitational-wave observations in the future.