The cosmological impact of future constraints on $H_0$ from gravitational-wave standard sirens

TL;DR

Future gravitational-wave standard sirens, combined with CMB and BAO data, can significantly refine measurements of the Hubble constant and other cosmological parameters, impacting our understanding of dark energy and universe curvature.

Contribution

This paper evaluates the potential of future gravitational-wave standard siren measurements to improve constraints on $H_0$, dark energy, and curvature in cosmological models.

Findings

Future standard sirens could measure $H_0$ to 1% accuracy.

Combining GW data with CMB+BAO tightens constraints on cosmological parameters.

GW $H_0$ measurements could reduce dark energy figure-of-merit by up to 400.

Abstract

Gravitational-wave standard sirens present a novel approach for the determination of the Hubble constant. After the recent spectacular confirmation of the method thanks to GW170817 and its optical counterpart, additional standard siren measurements from future gravitational-wave sources are expected to constrain the Hubble constant to high accuracy. At the same time, improved constraints are expected from observations of cosmic microwave background (CMB) polarization and from baryon acoustic oscillations (BAO) surveys. We explore the role of future standard siren constraints on $H_0$ in light of expected CMB+BAO data. Considering a $10$-parameters cosmological model, in which curvature, the dark energy equation of state, and the Hubble constant are unbounded by CMB observations, we find that a combination of future CMB+BAO data will constrain the Hubble parameter to $\sim 1.5 \%$. Further extending the parameter space to a time-varying dark energy equation of state, we find that future CMB+BAO constraints on $H_0$ are relaxed to $\sim 3.0 \%$. These accuracies are within reach of future standard siren measurements from the Hanford-Livingston-Virgo and the Hanford-Livingston-Virgo-Japan-India networks of interferometers, showing the cosmological relevance of these sources. If future gravitational-wave standard siren measurements reach $1\%$ on $H_0$, as expected, they would significantly improve future CMB+BAO constraints on curvature and on the dark energy equation of state by up to a factor $\sim 3$. We also show that the inclusion of $H_0$ constraints from gravitational-wave standard sirens could result in a reduction of the dark energy figure-of-merit (i.e., the cosmological parameter volume) by up to a factor of $\sim 400$.