Probing cosmic strings with gravitational-wave fringe

Abstract

Cosmic strings are important remnants of early-Universe phase transitions. We show that they can be probed by Gravitational Waves (GWs) from compact binary mergers. If such chirping GW passes by a cosmic string, it is gravitationally lensed and left with a characteristic signal of the lensing—the GW fringe. It is observable naturally through the frequency chirping of GWs. This allows to probe cosmic strings with small tension Δ = 8π G μ = 10−6 − 10−10, just below the current constraint, at high-frequency LIGO-band and mid-band detectors. Although its detection rates are estimated to be small, even a single detection can be used to identify a cosmic string. Contrary to the stochastic GW produced from loop decays only in local U(1) models, the GW fringe can directly probe straight strings model independently. This is also complementary to the existing probes with the strong lensing of light.