Probing cosmic strings via gravitational-wave lensing

TL;DR

This paper develops a new framework for detecting gravitational-wave signals lensed by cosmic strings, which could reveal insights into high-energy physics and the early Universe, by analyzing distinctive diffraction and interference patterns.

Contribution

It introduces an analytical full-wave lensing model for cosmic strings, contrasting it with point mass lensing, and demonstrates how to distinguish cosmic string lensing in gravitational-wave data.

Findings

Cosmic string lensing produces characteristic beating patterns in waveforms.

The framework can differentiate cosmic string lensing from unlensed and point mass lensing.

Detectability bounds on string tension are established.

Abstract

We present a framework for detecting gravitational-wave signals lensed by cosmic strings (CSs), addressing a key gap in current searches. CSs, whose detection would provide a unique probe of high-energy physics and the early Universe, possess distinct topological and geometric features that require a dedicated search strategy. Our approach employs a full-wave transmission factor, expressed analytically via Fresnel integrals, which captures the characteristic diffraction and interference effects of the conical spacetime around a straight CS. We contrast CS lensing with the well-studied point mass lens (PML) model, highlighting their fundamental differences: CS lensing depends on cosmological distances, string tension $\Delta$, and wavelength $\lambda$, and produces two non-amplified images set by the global conical geometry. In contrast, PML lensing is governed by the distance-independent ratio $\sim M_{Lz}/\lambda$, where $M_{Lz}$ represents the redshifted mass of the lens, with image properties derived from the lens equation. For BBH mergers lensed by CSs, we show that the waveforms exhibit a characteristic beating pattern or time-separated exact replicas. We derive a detectability bound on the string tension and, using Bayesian model selection, demonstrate that CS lensing is distinguishable from both unlensed and PML-lensed signals across a wide region of parameter space.