Ability of LISA to detect a gravitational-wave background of cosmological origin: the cosmic string case

TL;DR

This paper assesses LISA's capability to detect and estimate the properties of a gravitational-wave background from cosmic strings amid various noise sources, demonstrating potential measurement of string tension in the range of 10^{-16} to 10^{-15}.

Contribution

It introduces a comprehensive analysis using Fisher and MCMC methods to evaluate LISA's ability to distinguish cosmic string signals from noise and foregrounds, including parameter estimation techniques applicable to other backgrounds.

Findings

LISA can potentially measure cosmic string tension Gμ in the range 10^{-16} to 10^{-15}.

Galactic foregrounds significantly impact the detection limits.

Parameter estimation methods are adaptable to other cosmological backgrounds.

Abstract

We investigate the ability of the Laser Interferometer Space Antenna (LISA) to detect a stochastic gravitational-wave background (GWB) produced by cosmic strings, and to subsequently estimate the string tension $G\mu$ in the presence of instrument noise, an astrophysical background from compact binaries, and the galactic foreground from white dwarf binaries. Fisher Information and Markov Chain Monte Carlo methods provide estimates of the LISA noise and the parameters for the different signal sources. We demonstrate the ability of LISA to simultaneously estimate the galactic foreground, as well as the astrophysical and cosmic string produced backgrounds. Considering the expected astrophysical background and a galactic foreground, a cosmic string tension in the $G \mu \approx 10^{-16}$ to $G\mu \approx 10^{-15}$ range or bigger could be measured by LISA, with the galactic foreground affecting this limit more than the astrophysical background. The parameter estimation methods presented here can be applied to other cosmological backgrounds in the LISA observation band.