Higher signal harmonics, LISA's angular resolution, and dark energy

TL;DR

Including higher signal harmonics in LISA's analysis significantly improves its ability to pinpoint the host galaxy of binary SMBHs, enabling better dark energy constraints.

Contribution

This paper demonstrates that higher harmonics enhance LISA's angular resolution, making host galaxy identification feasible and improving dark energy measurements.

Findings

Angular resolution improves by over a factor of 10 with higher harmonics.

LISA can constrain dark energy parameters to a few percent.

Host galaxy identification becomes possible for certain SMBH binaries.

Abstract

It is generally believed that the angular resolution of the Laser Interferometer Space Antenna (LISA) for binary supermassive black holes (SMBH) will not be good enough to identify the host galaxy or galaxy cluster. This conclusion, based on using only the dominant harmonic of the binary SMBH signal, changes substantially when higher signal harmonics are included in assessing the parameter estimation problem. We show that in a subset of the source parameter space the angular resolution increases by more than a factor of 10, thereby making it possible for LISA to identify the host galaxy/galaxy cluster. Thus, LISA's observation of certain binary SMBH coalescence events could constrain the dark energy equation of state to within a few percent, comparable to the level expected from other dark energy missions.