The Laser Interferometer Space Antenna (LISA) mission will be capable of not only detecting but also characterizing the properties of metastable cosmic string networks. A new study has analyzed LISA's ability to reconstruct the parameters of these strings, such as their tension ($G\mu$) and metastability scale ($\kappa_{\rm CS}$), from the stochastic gravitational-wave backgrounds they would generate.

Metastable cosmic strings, unlike stable ones, decay over time. This decay, occurring via the nucleation of monopole pairs, suppresses loop production and leads to a network collapse. This finite lifetime process imprints a distinctive signature on the gravitational-wave spectrum: an infrared tail and a transition towards a high-frequency plateau, similar to that of stable strings. Detecting this spectral transition within the LISA band is crucial for parameter reconstruction.

Using synthetic LISA data that includes instrumental noise and unresolved astrophysical foregrounds, researchers performed a Bayesian analysis in the ($G\mu, \kappa_{\rm CS}$) parameter space. The results indicate that when LISA samples the transition between the infrared tail and the high-frequency plateau, the data contain sufficient amplitude and shape information to recover the string tension and metastability scale. Even in scenarios where the transition is not prominent, high signal-to-noise ratio spectra can retain partial sensitivity to $\kappa_{\rm CS}$ due to residual lifetime dependence. The study also assessed sensitivity to Galactic foreground modeling by comparing flexible templates with reduced templates.

This work demonstrates that LISA has the potential to move beyond mere detection of gravitational-wave backgrounds from cosmic strings, enabling detailed characterization of their lifetime and fundamental properties. This will open a new window for exploring early universe physics and grand unification theories that predict the existence of these topological structures.