Blinded Mock Data Challenge: Is the Spectral Siren Technique Robust for Measuring the Hubble Constant?

TL;DR

This paper evaluates the spectral siren technique's robustness in measuring the Hubble constant using gravitational wave data, emphasizing the importance of accurately modeling the BBH mass distribution across redshifts.

Contribution

It demonstrates through a blinded mock data challenge that capturing the metallicity dependence of BBH mass distribution is crucial for reliable Hubble constant inference.

Findings

Accurate modeling of BBH mass distribution across redshifts is essential.

Mismatch in the assumed and true models can bias the Hubble constant measurement.

Independent inference of BBH mass distribution must reach less than statistical uncertainty.

Abstract

The measurement of the Hubble constant from gravitational wave (GW) sources is one of the independent avenues to shed light on the Hubble tension, which is associated with about an $8\%$ mismatch in the value of the Hubble constant inferred from low-redshift and high-redshift cosmological probes. Such a key measurement is expected from GW sources as it is a direct measurement of the Hubble constant using the luminosity distance without the need for any luminosity distance calibration. However, such a measurement relies strongly on the reliability of the independent inference of the source redshift of the GW source. As a result, it becomes pertinent to gauge the accuracy and precision of techniques in understanding their reliability in inferring redshifts of GW sources. In this work, we show the requirement of the spectral siren technique in knowing the mass distribution of BBHs across cosmic redshifts in order to make a reliable inference of the Hubble constant. We show by a blinded mock data challenge analysis the criticality in capturing the underlying metallicity dependence of the BBH mass distribution and its interplay with time-delay distribution for a robust inference of the Hubble constant using the spectral siren technique. In order to have a reliable measurement of the Hubble constant at the level required to resolve the Hubble tension in the future, the mass distribution of the BBHs needs to be independently inferred at all relevant redshifts with an accuracy less than the statistical uncertainty. Otherwise, a mismatch of the true model and the underlying assumption made in the analysis can lead to a best-fit model for the wrong value of both BBH population parameters as well as the Hubble constant.