Gravitational lensing of Continuous Gravitational Waves

TL;DR

This paper reviews gravitational lensing effects on continuous gravitational waves, discussing theoretical regimes, observable interference phenomena, and potential applications for future detectors and black hole searches.

Contribution

It provides a comprehensive overview of gravitational lensing theory for gravitational waves in geometric and wave optics regimes, highlighting observable effects and new detection possibilities.

Findings

Interference causes beat patterns in gravitational waves detectable by future observatories.

Wave optics effects like diffraction could reveal properties of lensing systems.

Diffractive microlensing offers a method to find intermediate mass black holes.

Abstract

Continuous gravitational waves are analogous to monochromatic light and therefore could be used to detect wave effects like interference or diffraction. This would be possible with strongly lensed gravitational waves. This article reviews and summaries the theory of gravitational lensing in the context of gravitational waves in two different regimes: geometric optics and wave optics, for two widely used lens models such as point mass lens and Singular Isothermal Sphere (SIS). Observable effects due to wave nature of gravitational waves are discussed. As a consequence of interference GWs produce beat patterns which might be observable with the next generation detectors like ground based Einstein Telescope, Cosmic Explorer or space-borne LISA, DECIGO. This will provide us a opportunity to estimate the properties of lensing system and other cosmological parameters with alternative techniques. Diffractive microlensing could become a valuable method to search for intermediate mass black holes formed in the centers of globular clusters. We also point to an interesting idea of detecting the Poisson-Arago spot proposed in the literature.