This paper asks whether the Laser Interferometer Space Antenna (LISA) could do more than detect a cosmological gravitational-wave background. The authors focus on a specific source: metastable cosmic strings that decay by nucleating monopole–antimonopole pairs on the string. In the standard “vacuum-tunneling” picture they study, the network lives for a finite time and that lifetime leaves a clear imprint on the sound of the sky — a low-frequency “infrared” tail and a transition to a high-frequency plateau in the gravitational-wave spectrum.

To test what LISA could learn, the researchers build realistic mock LISA data. They include instrumental noise, the planned three-spacecraft LISA geometry with 2.5×10^6 km arms, and the main unresolved astrophysical foregrounds such as the Galactic population of double white-dwarf binaries and extragalactic compact binaries. They then run a Bayesian parameter-recovery analysis for two parameters: the string tension Gμ, which mainly sets the signal amplitude, and the metastability parameter κ_CS, which controls the network decay time and therefore the spectral shape.

Their main finding is simple and intuitive. If LISA’s frequency band catches the broad lifetime-dependent transition between the infrared tail and the plateau, the data contain both amplitude and shape information. In that case the two physical parameters can be recovered, although the recovered values can be strongly correlated: the data may pin down a narrow combination of amplitude and lifetime while leaving uncertainty along a trade-off direction. If instead the spectrum looks featureless in the LISA band — for example if only the plateau or only the tail is observed — then the instrument mostly measures a single amplitude-like combination and the metastability parameter becomes hard to identify.