A measurement of $H_0$ from DESI DR1 using energy densities

TL;DR

This work presents a novel, pre-recombination–independent measurement of the Hubble constant $H_0$ by anchoring the present critical density to the photon density and anchoring the baryon content with BBN while extracting the matter fraction from galaxy clustering. The method computes the present critical density via $\epsilon_c = \epsilon_{\gamma,0} \times (\epsilon_{b,0}/\epsilon_{\gamma,0}) \times (\epsilon_{m,0}/\epsilon_{b,0}) \times (1/\Omega_{m,0})$ and compares it to the geometric $\Omega_m$ to derive $H_0$, using $\gamma_b$ to robustly infer the baryon fraction from growth. The authors validate the approach on $N$-body mocks in $\Lambda$CDM and Early Dark Energy (EDE) cosmologies and apply it to DESI DR1 data, combined with the angular CMB scale $\theta_\star$ and BBN constraints, obtaining $H_0 = 69.0 \pm 2.5$ km s$^{-1}$ Mpc$^{-1}$. The results are consistent with both early- and late-time determinations and demonstrate resilience to modifications of the sound horizon, offering a powerful cross-check of the Hubble tension that will benefit from future DESI and Euclid data releases. The analysis uses two pipelines (full-shape EFT and post-reconstruction BAO) to extract the baryon fraction, with cross-validation showing concordant $H_0$ constraints and robust handling of nuisance parameters through HOD-informed priors.

Abstract

We present a new measurement of the Hubble constant, independent of standard rulers and robust to pre-recombination modifications such as Early Dark Energy (EDE), obtained by calibrating the total energy density of the Universe. We start using the present-day photon density as an anchor, and use the baryon-to-photon ratio from Big Bang Nucleosynthesis based measurements and the baryon-to-matter ratio from the baryons' imprint on galaxy clustering to translate to a physical matter density at present day. We then compare this to measurements of the ratio of the matter density to the critical density ($Ω_{\mathrm{m}}$), calculated using the relative positions of the baryon acoustic oscillations, to measure the critical density of the universe and hence $H_0$. The important measurements of the evolution of the energy density all happen at low redshift, so we consider this a low-redshift measurement. We validate our method both on a suite of $N$-body mocks and on noiseless theory vectors generated across a wide range of Hubble parameters in both $Λ$CDM and EDE cosmologies. Using DESI DR1 data combined with the angular CMB acoustic scale and the latest BBN constraints, we find $H_0 = 69.0 \pm 2.5$ km s$^{-1}$ Mpc$^{-1}$, consistent with existing early and late-time determinations of the Hubble constant. We consider the impact of non-standard dark energy evolution on our measurement. Future data, including that from further iterations of DESI and from Euclid, will add to these results providing a powerful test of the Hubble tension.

Figures (12)

• Figure 1: Constraints on $\Lambda$CDM parameters and the Hubble parameter $h^{\textrm{dens}}$ derived from the combination of energy densities, using the mean of the 25 Abacus mocks (truth in dashed lines). The red crosses show the maximum of the posterior. Black dots show marginalized means from the individual mocks.
• Figure 2: Our method accurately recovers the Hubble parameter across a wide range in true $h$, and in both a $\Lambda$CDM and an Early Dark Energy cosmology (with $h = 0.722$).
• Figure 3: The recovery of $\gamma_b$ and $h^{\textrm{dens}}$ on the pre-reconstruction power spectrum is not sensitive to the details of IR resummation. Here we compare the default result (on the mean of the 25 Abacus mocks) to runs where we change the filter used to construct the no-wiggle power spectrum (orange) or those where we change the damping of the wiggle power spectrum (green and purple).
• Figure 4: Distribution of $\gamma_b$ fit to the post-reconstruction correlation function of all DESI tracers in the 25 Abacus mocks; the tracers are split between the two panels for clarity. The solid black line shows the true value of the baryon fraction and the dashed lines show the fits to the mean of the 25 Abacus mocks.
• Figure 5: Comparison between Alcock-Paczynski parameters, $\alpha_{\textrm{iso}}$ and $\alpha_{\textrm{AP}}$, from the default DESI fits to the post-reconstruction correlation function, and fit using our pipeline with $\gamma_b$ as a free parameter. Blue dots show the fit to each of the 25 Abacus mocks, while the red star shows the fit to the mean. The BAO amplitude fits have been rescaled to match the DESI fiducial cosmology. The dashed line indicates perfect agreement between the two pipelines.