Spectral separation of the stochastic gravitational-wave background for LISA: observing both cosmological and astrophysical backgrounds

TL;DR

This paper evaluates LISA's ability to distinguish and detect the cosmological gravitational wave background amidst astrophysical signals using advanced statistical methods and simulated data.

Contribution

It introduces a comprehensive analysis of spectral separation capabilities for LISA, combining MCMC and Fisher analysis to estimate detection limits for cosmological backgrounds.

Findings

LISA can detect a cosmological background with energy density around 10^{-12} to 10^{-13}.

Spectral separation between cosmological and astrophysical backgrounds is feasible with current models.

Advanced statistical methods improve parameter estimation accuracy.

Abstract

With the goal of attempting to observe a stochastic gravitational wave background (SGWB) with LISA, the spectral separability of the cosmological and astrophysical backgrounds is important to estimate. We attempt to determine the level with which a cosmological background can be observed given the predicted astrophysical background level. We predict detectable limits for the future LISA measurement of the SGWB. Adaptive Markov chain Monte-Carlo methods are used to produce estimates with the simulated data from the LISA Data challenge (LDC). We also calculate the Cramer-Rao lower bound on the variance of the SGWB parameter uncertainties based on the inverse Fisher Information using the Whittle Likelihood. The estimation of the parameters is done with the 3 LISA channels $A$, $E$, and $T$. We simultaneously estimate the noise using a LISA noise model. Assuming the expected astrophysical background, a cosmological background energy density of around $\Omega_{GW,Cosmo} \approx 1 \times 10^{-12}$ to $1 \times 10^{-13}$ can be detected by LISA.