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Prospects for resolving the Hubble constant tension with standard sirens

Stephen M. Feeney, Hiranya V. Peiris, Andrew R. Williamson, Samaya M. Nissanke, Daniel J. Mortlock, Justin Alsing, Dan Scolnic

TL;DR

The paper addresses the $H_0$ tension between the local Cepheid-SN distance ladder and CMB-based inferences under ΛCDM by introducing a model-agnostic framework using the posterior predictive distribution (PPD) and the inverse distance ladder built from BAO and Pantheon SN data. It finds that the inverse distance ladder yields $H_0$ values in close agreement with Planck, while the SH0ES measurement is unlikely under that joint posterior, indicating persistent tension. The authors quantify this tension with PPD ratios (e.g., $\rho \approx 0.06$ for SH0ES and $\rho \approx 0.022$ for Planck) and propose that approximately 50 binary neutron star standard sirens could decisively arbitrate between the Planck and SH0ES values within a decade, though realization noise can affect the exact sample size required. The work highlights a concrete, model-light path to resolve the tension using independent standard siren data and careful probabilistic tension diagnostics.

Abstract

The Hubble constant ($H_0$) estimated from the local Cepheid-supernova (SN) distance ladder is in 3-$σ$ tension with the value extrapolated from cosmic microwave background (CMB) data assuming the standard cosmological model. Whether this tension represents new physics or systematic effects is the subject of intense debate. Here, we investigate how new, independent $H_0$ estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (PPD). We show that, with existing data, the inverse distance ladder formed from BOSS baryon acoustic oscillation measurements and the Pantheon SN sample yields an $H_0$ posterior near-identical to the Planck CMB measurement. The observed local distance ladder value is a very unlikely draw from the resulting PPD. Turning to the future, we find that a sample of $\sim50$ binary neutron star "standard sirens" (detectable within the next decade) will be able to adjudicate between the local and CMB estimates.

Prospects for resolving the Hubble constant tension with standard sirens

TL;DR

The paper addresses the tension between the local Cepheid-SN distance ladder and CMB-based inferences under ΛCDM by introducing a model-agnostic framework using the posterior predictive distribution (PPD) and the inverse distance ladder built from BAO and Pantheon SN data. It finds that the inverse distance ladder yields values in close agreement with Planck, while the SH0ES measurement is unlikely under that joint posterior, indicating persistent tension. The authors quantify this tension with PPD ratios (e.g., for SH0ES and for Planck) and propose that approximately 50 binary neutron star standard sirens could decisively arbitrate between the Planck and SH0ES values within a decade, though realization noise can affect the exact sample size required. The work highlights a concrete, model-light path to resolve the tension using independent standard siren data and careful probabilistic tension diagnostics.

Abstract

The Hubble constant () estimated from the local Cepheid-supernova (SN) distance ladder is in 3- tension with the value extrapolated from cosmic microwave background (CMB) data assuming the standard cosmological model. Whether this tension represents new physics or systematic effects is the subject of intense debate. Here, we investigate how new, independent estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (PPD). We show that, with existing data, the inverse distance ladder formed from BOSS baryon acoustic oscillation measurements and the Pantheon SN sample yields an posterior near-identical to the Planck CMB measurement. The observed local distance ladder value is a very unlikely draw from the resulting PPD. Turning to the future, we find that a sample of binary neutron star "standard sirens" (detectable within the next decade) will be able to adjudicate between the local and CMB estimates.

Paper Structure

This paper contains 6 sections, 16 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Quantifying Tension
  3. Arbitrating Tension With Standard Sirens
  4. Conclusions
  5. Acknowledgments
  6. Analytic Standard Siren Posterior Derivation

Figures (4)

  • Figure 1: Main panel: expansion history for BOSS BAO, Pantheon SNe and Planck$r_{\rm d}$ assuming smooth expansion and early-time physics only (blue), and for Planck assuming $\Lambda$CDM (grey). BAO redshifts are shown as short-dashed lines. Left panel: corresponding $H_0$ posteriors and Cepheid distance ladder measurement (orange). Top panel: redshift distribution of Pantheon SNe.
  • Figure 2: PPDs (shaded) for the Cepheid distance ladder $\hat{H}_0$, conditioned on inverse distance ladder data assuming a smooth expansion history (blue) or CMB data assuming $\Lambda$CDM (grey). The SH0ES measurement is plotted as an orange solid line, and the $H_0$ posteriors from which the PPDs derive are plotted as dashed lines.
  • Figure 3: $H_0$ posteriors for individual BNS mergers (purple to yellow, sorted by signal-to-noise) and the full sample (black solid; scaled by a factor of 1/3), assuming a true $H_0$ of 67.81 ${\rm km\,s^{-1}\,Mpc^{-1}}$ (black dashed).
  • Figure 4: PPDs for the CMB (dark blue) and Cepheid distance ladder (dark orange) $\hat{H}_0$ measurements, given the simulated BNS data. Solid/dashed curves assume the true $H_0$ to be the Planck/SH0ES measured value, indicated by the light blue/orange solid line. The 1-$\sigma$ variations in PPD means due to sample variance are shaded grey.