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arxiv: 2606.05358 · v1 · pith:ZVSN2POOnew · submitted 2026-06-03 · 🌌 astro-ph.CO

The DESI results impact the local determination of H₀

Michael S. Turner , Dragan Huterer This is my paper

Pith reviewed 2026-06-28 04:33 UTC · model grok-4.3

classification 🌌 astro-ph.CO
keywords DESIHubble constantdark energyBAOw0waHubble tensioncosmologydistance ladder
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The pith

DESI-favored dark energy models reduce the locally determined Hubble constant by as much as 2.5 km/s/Mpc compared to LambdaCDM.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that the Hubble constant value extracted from local distance measurements changes when a different background cosmology is assumed. Replacing the standard LambdaCDM model with the w0wa dark energy parametrization preferred by DESI baryon acoustic oscillation data produces a downward shift in H0 of up to 2.5 km s^{-1} Mpc^{-1}. Adding constraints from cosmic microwave background and supernova observations reduces but does not eliminate the shift. A sympathetic reader would care because the result ties the Hubble tension to uncertainty in the low-redshift expansion history rather than to early-universe physics alone.

Core claim

If local distance measurements are analyzed with the w0wa models preferred by the DESI measurements, the value for the Hubble constant can be as much as 2.5 km s^{-1} Mpc^{-1} smaller than the value obtained assuming LambdaCDM. When these w0wa models are further constrained by cosmic microwave background (CMB) and type Ia supernova (SNIa) data, the downward shift is 1.1 ± 0.38 km s^{-1} Mpc^{-1} (DESI + CMB) and 0.5 ± 0.1 km s^{-1} Mpc^{-1} (DESI + CMB + SNIa). The dependence of local determinations of H0 on the background cosmology, combined with the fact that the low-redshift cosmology is not well constrained, is relevant to the Hubble tension.

What carries the argument

The w0wa parametrization of dark energy, which sets a time-varying equation-of-state and thereby changes the low-redshift expansion history used to convert local distance-ladder observables into an H0 value.

If this is right

  • Local H0 determinations become sensitive to the assumed dark energy model at low redshift.
  • DESI-preferred w0wa models produce an H0 value up to 2.5 km s^{-1} Mpc^{-1} lower than LambdaCDM.
  • Adding CMB data limits the downward shift to 1.1 ± 0.38 km s^{-1} Mpc^{-1}.
  • Further adding SNIa data reduces the shift to 0.5 ± 0.1 km s^{-1} Mpc^{-1}.
  • This model dependence is directly relevant to interpreting the Hubble tension.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Standard future analyses of the distance ladder should default to evolving dark energy models if DESI results hold.
  • Part of the current Hubble tension may reflect the use of an incorrect low-redshift cosmology rather than new early-universe physics.
  • Tighter low-redshift constraints on w0 and wa from upcoming surveys would directly test the size of the reported H0 shift.

Load-bearing premise

The w0wa parametrization and parameter values favored by DESI BAO data constitute an appropriate background cosmology for re-deriving H0 from local distance-ladder observations.

What would settle it

Re-deriving the local H0 value with the exact DESI best-fit w0 and wa parameters and finding no shift relative to the LambdaCDM result would falsify the reported downward correction.

Figures

Figures reproduced from arXiv: 2606.05358 by Dragan Huterer, Michael S. Turner.

Figure 1
Figure 1. Figure 1: FIG. 1. Luminosity distance vs. redshift for: [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. The lines show the dependence of [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: shows the expansion rate for three w0wa models consistent with the DESI results. Thinking more broadly about changes in the cosmology at low redshift, consider dark energy that monotonically decreases, as might be the case with a thawing scalar 3 Because the DR2 alone ellipse does not close, the prior wa ≥ −3 was imposed, limits the shift in HDN 0 4 3 2 1 0 wa 71.0 71.5 72.0 72.5 73.0 73.5 I n fe r r e d H… view at source ↗
read the original abstract

Measurements of baryon acoustic oscillations (BAO) by the Dark Energy Spectroscopic Instrument (DESI) have revealed evidence for dark energy that evolves. If local distance measurements are analyzed with the $w_0w_a$ models preferred by the DESI measurements, the value for the Hubble constant can be as much as $2.5\,\mathrm{km\,s^{-1}Mpc^{-1}}$ smaller than the value obtained assuming $\Lambda$CDM. When these $w_0w_a$ models are further constrained by cosmic microwave background (CMB) and type Ia supernova (SNIa) data, the downward shift is $1.1 \pm 0.38\,\mathrm{km\,s^{-1}Mpc^{-1}}$ (DESI + CMB) and $0.5 \pm 0.1\,\mathrm{km\,s^{-1}Mpc^{-1}}$ (DESI + CMB + SNIa). The dependence of local determinations of $H_0$ on the background cosmology, combined with the fact that the low-redshift cosmology is not well constrained, is relevant to the Hubble tension.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript claims that re-analyzing local distance-ladder observations under the w0wa dark-energy parametrization favored by DESI BAO data yields a lower best-fit H0 than the standard LambdaCDM assumption, with a maximum downward shift of 2.5 km s^{-1} Mpc^{-1} for DESI-only constraints; the shift reduces to 1.1 ± 0.38 km s^{-1} Mpc^{-1} when CMB data are added and to 0.5 ± 0.1 km s^{-1} Mpc^{-1} for the DESI+CMB+SNIa combination. The dependence of the local H0 inference on the assumed low-redshift expansion history is presented as relevant to the Hubble tension.

Significance. If the quoted shifts are reproducible, the result illustrates that local H0 determinations are not cosmology-independent at the level of current precision and that the specific w0wa models preferred by DESI can move the local value closer to early-universe inferences. The paper supplies concrete numerical estimates for three data combinations, thereby quantifying one possible contribution to the tension that arises purely from the choice of background model.

major comments (1)
  1. [Abstract] Abstract and main text: the numerical H0 shifts (2.5, 1.1 ± 0.38, 0.5 ± 0.1 km s^{-1} Mpc^{-1}) are stated without any derivation, explicit integral for luminosity distance, list of local distance-ladder data, adopted w0wa parameter values, or error-budget breakdown. Because these numbers constitute the central claim, the absence of the calculation prevents verification that the reported uncertainties are correctly propagated from the external DESI constraints.
minor comments (1)
  1. The manuscript would benefit from a short methods paragraph or appendix that reproduces the luminosity-distance integral and states the precise local data cuts and fitting procedure used to obtain the quoted shifts.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their report and for highlighting the need for greater transparency in the derivation of our central results. We agree that the manuscript would benefit from explicit details on the calculation and will revise accordingly to address this concern.

read point-by-point responses

  1. Referee: [Abstract] Abstract and main text: the numerical H0 shifts (2.5, 1.1 ± 0.38, 0.5 ± 0.1 km s^{-1} Mpc^{-1}) are stated without any derivation, explicit integral for luminosity distance, list of local distance-ladder data, adopted w0wa parameter values, or error-budget breakdown. Because these numbers constitute the central claim, the absence of the calculation prevents verification that the reported uncertainties are correctly propagated from the external DESI constraints.

    Authors: We agree that the derivation must be shown explicitly. In the revised manuscript we will add a dedicated methods section that (i) states the luminosity-distance integral d_L(z) = (1+z)∫_0^z c dz'/[H_0 E(z')] with the standard w_0w_a expression for E(z), (ii) lists the local distance-ladder data (Cepheid-calibrated SN Ia from the SH0ES compilation) and the exact reference, (iii) quotes the adopted (w_0, w_a) central values and covariance matrices taken from the three DESI analyses (BAO-only, BAO+CMB, BAO+CMB+SNIa), and (iv) describes the error propagation: the local H_0 posterior is obtained by marginalizing the distance-ladder likelihood over the external w_0w_a posterior, yielding the quoted shifts and uncertainties. These additions will allow direct reproduction of the numbers. revision: yes

Circularity Check

0 steps flagged

No significant circularity identified

full rationale

The paper computes the shift in local H0 by inserting externally constrained w0wa expansion histories (from DESI BAO, plus optional CMB and SNIa) into the standard luminosity-distance integral applied to local distance-ladder data. This is a direct numerical consequence of the integral expression for d_L(z) under a different H(z); no equation inside the paper defines the output H0 value in terms of itself or renames a fitted parameter as a prediction. No self-citation is invoked as a uniqueness theorem or load-bearing premise, and the central claim remains conditional on the external DESI constraints rather than internally forced.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on the domain assumption that DESI-derived w0wa models can be substituted into the local distance-ladder analysis without additional low-redshift systematics; no new free parameters or entities are introduced in the abstract.

axioms (1)
  • domain assumption The w0wa parametrization favored by DESI BAO data is a valid background cosmology for local H0 inference
    Central numerical shifts are obtained only after this substitution is performed.

pith-pipeline@v0.9.1-grok · 5732 in / 1321 out tokens · 36173 ms · 2026-06-28T04:33:29.108548+00:00 · methodology

discussion (0)

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Reference graph

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