The fault in our sirens: Hierarchical diagnosis of waveform systematics in Hubble-Lema\^itre constant measurements

TL;DR

This paper investigates how waveform modeling inaccuracies affect the measurement of the Hubble-Lemaître constant using gravitational-wave data, revealing that even small subpopulations can bias results in current and future observatories.

Contribution

It introduces a hierarchical diagnosis method to identify waveform systematic errors in cosmological measurements without prior knowledge of the true parameter value.

Findings

Small high-mass, spin-precessing subpopulations can bias Hubble constant measurements.

Inaccurate waveform models can lead to unreliable cosmological inferences.

Effects are more severe in future ground-based gravitational-wave observatories.

Abstract

Cosmological inference using a population of binary black-hole mergers, combined with a galaxy catalog, presents an exciting opportunity for precision cosmology with the possibility of resolving the Hubble tension. However, the accuracy of these measurements heavily relies on the quality of the model used to infer the binary parameters, including the model of the gravitational-wave signal. We use state-of-the-art waveform models to explore the impact of inaccurate modeling in measuring the Hubble-Lema\^itre constant for the upcoming and future ground-based gravitational-wave observatories. We diagnose the presence of inaccuracies within a hierarchical population-analysis framework, without a priori knowing the true value of the parameter, by assessing the consistency of the distribution of individual posteriors in relation to their measurement errors. Our findings indicate that even a small high-mass, spin-precessing subpopulation -- comprising as little as 5\% of the population generating the events observed by the LIGO-Virgo-KAGRA Collaboration so far -- can result in an unreliable measurement of the Hubble-Lema\^itre constant in the upcoming observing runs of these detectors, with even more pronounced effects expected in future facilities on the ground.