Weakly Lensed Gravitational Waves: Probing Cosmic Structures with Wave-Optics Features

TL;DR

This paper explores how wave-optics features in gravitational wave signals caused by weak lensing can reveal detailed information about cosmic structures, dark matter, and large-scale universe properties.

Contribution

It introduces an efficient framework to analyze wave-optics phenomena in gravitational waves, enabling detailed probing of substructures and dark matter through lensing signatures.

Findings

WOF can probe subhalo properties and inner profiles.

Upcoming detectors like LISA can observe WOF beyond Einstein radius.

Detection of WOF can test dark matter models.

Abstract

Every signal propagating through the universe is at least weakly lensed by the intervening gravitational field. In some situations, wave-optics phenomena (diffraction, interference) can be observed as frequency-dependent modulations of the waveform of gravitational waves (GWs). We will denote these signatures as Wave-Optics Features (WOFs) and analyze them in detail. Our framework can efficiently and accurately compute WOF in the single-image regime, of which weak lensing is a limit. The phenomenology of WOF is rich and offers valuable information: the dense cusps of individual halos appear as peaks in Green's function for lensing. If resolved, these features probe the number, effective masses, spatial distribution and inner profiles of substructures. High signal-to-noise GW signals reveal WOFs well beyond the Einstein radius, leading to a fair probability of observation by upcoming detectors such as LISA. Potential applications of WOF include reconstruction of the lens' projected density, delensing standard sirens and inferring large-scale structure morphology and the halo mass function. Because WOF are sourced by light halos with negligible baryonic content, their detection (or lack thereof) holds promise to test dark matter scenarios.