Cosmic string gravitational wave backgrounds at LISA: I. Signal survey, template reconstruction, and model comparison

TL;DR

This paper catalogs cosmic string gravitational wave background templates, assesses LISA's ability to reconstruct signals and distinguish models, and compares conventional and beyond-conventional cosmic string models.

Contribution

It provides a comprehensive catalog of cosmic string GW templates and evaluates LISA's precision in reconstructing and differentiating these signals across various models.

Findings

LISA can reconstruct the string tension Gμ with less than 10% error for Gμ > 5×10⁻¹⁵.

BOS and VOS models are distinguishable for Gμ > 5×10⁻¹³.

Beyond-conventional signals can be identified and separated from conventional ones within certain SNR thresholds.

Abstract

We present a catalog of gravitational wave background (GWB) signal templates from cosmic-string networks, based on relevant models proposed in the literature. We classify templates as conventional, based on standard cosmology and Nambu-Goto results (VOS and BOS), and beyond conventional, based on modifications of a) the loop number density (LRS, super, metastable, current-carrying strings), b) the expansion history (non-standard cosmologies, extra degrees of freedom, either thermal or secluded), or c) the loop properties (birth length, power emission). Using the SBI package $\texttt{GWBackFinder}$, we quantify the reconstruction precision of each signal by LISA, scanning over their parameter space, and performing model comparisons. For conventional signals, LISA reconstructs the tension $G\mu$ with an error $\lesssim 10\%$ for $G\mu \gtrsim 5\cdot 10^{-15}$, which decreases down to $2-3\%$ for $G\mu \gtrsim 10^{-12}$. BOS and VOS modelings become distinguishable confidently for $G\mu \gtrsim 5\cdot 10^{-13}$. For beyond-conventional signals, we identify SNR and error-threshold intervals for each parameter, and determine (for few examples) the regions where they can be distinguished from conventional signals. Analogous quality reconstruction studies of cosmic-string GWBs, superimposed over leading astrophysical foregrounds in the LISA window, will be presented in a series of upcoming papers.