LISA as a dark energy probe

TL;DR

This paper explores how LISA's enhanced parameter estimation capabilities, especially with higher harmonics, can be used to measure dark energy properties by analyzing gravitational wave signals from binary supermassive black holes.

Contribution

It demonstrates that LISA can constrain dark energy parameters, like the equation-of-state parameter, with high precision using gravitational wave observations of SMBH mergers.

Findings

LISA can measure the dark energy parameter w to within a few percent.

Including sky location in analysis improves w constraints by a factor of 2-3.

Weak lensing remains the main limitation in using LISA for dark energy studies.

Abstract

Recently it was shown that the inclusion of higher signal harmonics in the inspiral signals of binary supermassive black holes (SMBH) leads to dramatic improvements in parameter estimation with the Laser Interferometer Space Antenna (LISA). In particular, the angular resolution becomes good enough to identify the host galaxy or galaxy cluster, in which case the redshift can be determined by electromagnetic means. The gravitational wave signal also provides the luminosity distance with high accuracy, and the relationship between this and the redshift depends sensitively on the cosmological parameters, such as the equation-of-state parameter $w=p_{\rm DE}/\rho_{\rm DE}$ of dark energy. With a single binary SMBH event at $z < 1$ having appropriate masses and orientation, one would be able to constrain $w$ to within a few percent. We show that, if the measured sky location is folded into the error analysis, the uncertainty on $w$ goes down by an additional factor of 2-3, leaving weak lensing as the only limiting factor in using LISA as a dark energy probe.