Spin wave optics for gravitational waves lensed by a Kerr black hole

TL;DR

This paper investigates how gravitational waves are affected by lensing through a Kerr black hole, revealing spin-dependent oscillations in the wave amplification spectrum due to the interaction between wave properties and black hole spin.

Contribution

It introduces a numerical study of gravitational wave propagation through a Kerr black hole, highlighting the spin-dependent oscillatory effects in the wave amplification spectrum.

Findings

Helicity-dependent oscillations in the power spectrum

Oscillation amplitude increases with black hole spin

Enhanced effects for prograde Kerr black holes

Abstract

Gravitational waves exhibit the unique signature of their spin-2 nature in processes of wave scattering, due to the interaction between spin and a background spacetime. Since the spin effect is more pronounced for longer wavelengths and gravitational waves sourced by binaries have a long wavelength, it may become an important effect in addition to the wave effect. We study the propagation of gravitational waves lensed by a Kerr black hole by numerically solving the Teukolsky equation with a source term of the equal-mass circular binary, taking into account both spin effect and wave effect. We find helicity-dependent small-period oscillation in the power spectrum of the amplification factor in the forward direction and the oscillation is enhanced as spin of a prograde Kerr black hole increases.