DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations

TL;DR

DESI DR1 delivers high-precision BAO measurements across seven redshift bins from diverse tracers, enabling tight constraints on the expansion history and cosmological parameters. By combining DESI DR1 BAO with external priors on the sound horizon and CMB information, the study robustly constrains Ω_m, H0, curvature, and the neutrino sector, while testing dynamical dark energy through wCDM and w0w_aCDM extensions. The results broadly agree with ΛCDM in the baseline analysis but show mild preferences for evolving dark energy when SN Ia data are included, with tensions on the order of 2–4σ depending on datasets. Neutrino mass bounds tighten substantially in ΛCDM+∑m_ν, but weaken in extended models; N_eff is consistent with the standard value and shifts slightly with model freedom. Overall, DESI DR1 confirms the standard cosmology while enhancing the sensitivity to possible new physics in the late-time expansion and neutrino sector, setting the stage for even tighter constraints in the ongoing survey.

Abstract

We present cosmological results from the measurement of baryon acoustic oscillations (BAO) in galaxy, quasar and Lyman-$α$ forest tracers from the first year of observations from the Dark Energy Spectroscopic Instrument (DESI), to be released in the DESI Data Release 1. DESI BAO provide robust measurements of the transverse comoving distance and Hubble rate, or their combination, relative to the sound horizon, in seven redshift bins from over 6 million extragalactic objects in the redshift range $0.1<z<4.2$. DESI BAO data alone are consistent with the standard flat $Λ$CDM cosmological model with a matter density $Ω_\mathrm{m}=0.295\pm 0.015$. Paired with a BBN prior and the robustly measured acoustic angular scale from the CMB, DESI requires $H_0=(68.52\pm0.62)$ km/s/Mpc. In conjunction with CMB anisotropies from Planck and CMB lensing data from Planck and ACT, we find $Ω_\mathrm{m}=0.307\pm 0.005$ and $H_0=(67.97\pm0.38)$ km/s/Mpc. Extending the baseline model with a constant dark energy equation of state parameter $w$, DESI BAO alone require $w=-0.99^{+0.15}_{-0.13}$. In models with a time-varying dark energy equation of state parametrized by $w_0$ and $w_a$, combinations of DESI with CMB or with SN~Ia individually prefer $w_0>-1$ and $w_a<0$. This preference is 2.6$σ$ for the DESI+CMB combination, and persists or grows when SN~Ia are added in, giving results discrepant with the $Λ$CDM model at the $2.5σ$, $3.5σ$ or $3.9σ$ levels for the addition of Pantheon+, Union3, or DES-SN5YR datasets respectively. For the flat $Λ$CDM model with the sum of neutrino mass $\sum m_ν$ free, combining the DESI and CMB data yields an upper limit $\sum m_ν< 0.072$ $(0.113)$ eV at 95% confidence for a $\sum m_ν>0$ $(\sum m_ν>0.059)$ eV prior. These neutrino-mass constraints are substantially relaxed in models beyond $Λ$CDM. [Abridged.]

Figures (15)

• Figure 1: Top row: DESI measurements of the BAO distance scales at different redshifts, parametrised as (left) the ratio of the angle-averaged distance $D_\mathrm{V}\equiv(zD_\mathrm{M}^2D_\mathrm{H})^{1/3}$ to the sound horizon at the baryon drag epoch, $r_\mathrm{d}$, and (right) the ratio of transverse and line-of-sight comoving distances $F_\mathrm{AP}\equiv D_\mathrm{M}/D_\mathrm{H}$, from all tracers and redshift bins as labeled. For visual clarity and to compress the dynamic range of the plot, an arbitrary scaling of $z^{-2/3}$ has been applied on the left, and $z^{-1}$ on the right. The solid and dashed grey lines show model predictions from, respectively, the flat $\Lambda$CDM model that best fits this data, with $\Omega_\mathrm{m}=0.294$ and $H_0r_\mathrm{d}=1.0194\times10^4\;\mathrm{km\,s}^{-1}$, and from a $\Lambda$CDM model with parameters matching the Planck best-fit cosmology. The BGS and QSO data points appear only in the left panel and not the right one because the signal-to-noise ratio of the data is not yet sufficient to measure both parameters for these tracers. Bottom row: The same data points and models as in the top row, but now shown as the ratio relative to the predictions for the best-fit flat $\Lambda$CDM model.
• Figure 2: Left panel: 68% and 95% credible-interval contours for parameters $\Omega_\mathrm{m}$ and $r_\mathrm{d} h$ obtained for a flat $\Lambda$CDM model from fits to BAO measurements from each DESI tracer type individually, as labeled. Results from all tracers are consistent with each other and the change in the degeneracy directions arises from the different effective redshifts of the samples. Right panel: the corresponding results in flat $\Lambda$CDM for fits to BAO results from all DESI redshift bins (blue), the final SDSS results from Alam-eBOSS:2021 (orange), and the combination of these two as described in the text (green). The corresponding result from the CMB (including CMB lensing) is shown in pink.
• Figure 3: Left panel: marginalised posterior constraints on matter density $\Omega_\mathrm{m}$ and the Hubble constant $H_0$, obtained from combining DESI BAO data with external data used to calibrate the sound horizon $r_\mathrm{d}$, in a flat $\Lambda$CDM cosmological model. The combinations shown use a prior on $\omega_\mathrm{b}$ determined from BBN (blue), the combination of a BBN $\omega_\mathrm{b}$ prior and measurement of the acoustic angular scale $\theta_\ast$ (orange), and $r_\mathrm{d}$ directly calibrated from CMB results from Planck (green). The pink contour shows the corresponding constraints from the combination of CMB and CMB lensing. Right panel: The marginalised 1D posteriors on $\Omega_\mathrm{m}$ in flat $\Lambda$CDM, from DESI BAO, CMB and the three SN datasets, as labelled.
• Figure 4: 68% and 95% marginalised posterior constraints on $\Omega_\mathrm{m}$--$\Omega_\Lambda$ plane (left) and $\Omega_\mathrm{m}$--$\Omega_\mathrm{K}$ (right) in the one-parameter extension of the $\Lambda$CDM model with free curvature, $\Lambda$CDM$+\Omega_\mathrm{K}$. In the left panel the supernova contours are truncated at the lower-left by the $\mathcal{U}[-0.3, 0.3]$ prior on $\Omega_\mathrm{K}$.
• Figure 5: Constraints on $\Omega_\mathrm{m}$ and $w$ in the flat $w$CDM model. The constraints from DESI BAO alone are shown in blue, those from the CMB in pink, and different SN Ia compilations in solid and dashed green. The orange contour shows the combined constraint from DESI, CMB and PantheonPlus SN Ia. All contours show 68% and 95% credible intervals. Note the remarkable complementarity of cosmological probes in this plane.