Gravitational-Wave Fringes at LIGO: Detecting Compact Dark Matter by Gravitational Lensing

TL;DR

This paper demonstrates that LIGO can detect gravitational lensing effects caused by compact dark matter objects, providing a new method to probe small-scale universe structures using gravitational waves.

Contribution

It introduces a novel approach to detect lensing by compact dark matter with LIGO's existing capabilities, focusing on frequency-dependent amplification of GW signals.

Findings

LIGO can detect lensing by compact dark matter of $10 - 10^5 M_\u2299$.

One-year observation can constrain dark matter fraction to a few percent.

LIGO's sensitivity allows probing small-scale dark matter structures.

Abstract

Utilizing gravitational-wave (GW) lensing opens a new way to understand the small-scale structure of the universe. We show that, in spite of its coarse angular resolution and short duration of observation, LIGO can detect the GW lensing induced by compact structures, in particular by compact dark matter (DM) or primordial black holes of $10 - 10^5 \, M_\odot$, which remain interesting DM candidates. The lensing is detected through GW frequency chirping, creating the natural and rapid change of lensing patterns: \emph{frequency-dependent amplification and modulation} of GW waveforms. As a highest-frequency GW detector, LIGO is a unique GW lab to probe such light compact DM. With the design sensitivity of Advanced LIGO, one-year observation by three detectors can optimistically constrain the compact DM density fraction $f_{\rm DM}$ to the level of a few percent.