False positives for gravitational lensing: the gravitational-wave perspective

TL;DR

Detecting lensed gravitational waves is challenging due to false positives from coincident events, waveform degeneracies, and detector noise, requiring careful analysis and mitigation strategies.

Contribution

This paper reviews sources of false positives in gravitational-wave lensing searches and discusses methods to mitigate them, enhancing detection reliability.

Findings

False positives can arise from coincident unlensed events and waveform degeneracies.

Proper mitigation strategies are essential for reliable gravitational lensing detection.

Understanding detector noise is crucial for reducing false positives.

Abstract

For the first detection of a novel astrophysical phenomenon, scientific standards are particularly high. Especially in a multi-messenger context, there are also opportunity costs to follow-up observations on any detection claims. So in searching for the still elusive lensed gravitational waves, care needs to be taken in controlling false positives. In particular, many methods for identifying strong lensing rely on some form of parameter similarity or waveform consistency, which under rapidly growing catalog sizes can expose them to false positives from coincident but unlensed events if proper care is not taken. And searches for waveform deformations in all lensing regimes are subject to degeneracies we need to mitigate between lensing, intrinsic parameters, insufficiently modelled effects such as orbital eccentricity, or even deviations from general relativity. Robust lensing studies also require understanding and mitigating glitches and non-stationarities in the detector data. This article reviews sources of possible false positives (and their flip side: false negatives) in gravitational-wave lensing searches and the main approaches the community is pursuing to mitigate them.