Speaker
Description
Stochastic gravitational-wave backgrounds (SGWBs) from early-Universe topological defects offer a potential window into physics beyond the Standard Model. However, detecting a background does not necessarily mean that its underlying physical parameters can be independently reconstructed. This talk explores how spectral features, parameter degeneracies, and astrophysical foregrounds determine what the Laser Interferometer Space Antenna (LISA) may learn about these sources.
We first consider domain walls, whose gravitational-wave spectra encode information about the wall energy fraction and annihilation temperature. Using Bayesian reconstruction maps and a realistic LISA data model incorporating instrumental noise, Galactic double-white-dwarf confusion, and extragalactic compact-binary foregrounds, we identify the parameter-space regions where genuine two-parameter reconstruction is possible. We then discuss how combining pulsar timing array (PTA) information with LISA observations can alleviate degeneracies by probing different frequency ranges of the same spectrum.
Next, we turn to metastable cosmic strings, where finite network lifetimes imprint a characteristic spectral transition that can provide information about string tension and metastability. Finally, we examine cosmic superstrings, focusing on how the intercommutation probability can affect both the gravitational-wave amplitude and spectral shape, potentially enabling Bayesian discrimination between phenomenological models.
Across these examples, a common principle emerges: reconstruction depends not only on signal strength, but also on whether independent spectral information survives detector noise, foreground contamination, and parameter degeneracies. We discuss when LISA may move beyond detecting a stochastic background towards probing the underlying physics of early-Universe defects.