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Dark Energy Survey: implications for cosmological expansion models from the final DES Baryon Acoustic Oscillation and Supernova data

DES Collaboration, T. M. C. Abbott, M. Acevedo, M. Adamow, M. Aguena, A. Alarcon, S. Allam, O. Alves, F. Andrade-Oliveira, J. Annis, P. Armstrong, S. Avila, D. Bacon, K. Bechtol, J. Blazek, S. Bocquet, D. Brooks, D. Brout, D. L. Burke, H. Camacho, R. Camilleri, G. Campailla, A. Carnero Rosell, A. Carr, J. Carretero, F. J. Castander, R. Cawthon, K. C. Chan, C. Chang, R. Chen, C. Conselice, M. Costanzi, M. Crocce, L. N. da Costa, M. E. S. Pereira, T. M. Davis, J. De Vicente, N. Deiosso, S. Desai, H. T. Diehl, S. Dodelson, C. Doux, A. Drlica-Wagner, J. Elvin-Poole, S. Everett, I. Ferrero, A. Ferté, B. Flaugher, J. Frieman, L. Galbany, J. García-Bellido, M. Gatti, E. Gaztanaga, G. Giannini, D. Gruen, R. A. Gruendl, G. Gutierrez, W. G. Hartley, K. Herner, S. R. Hinton, D. L. Hollowood, K. Honscheid, D. Huterer, D. J. James, N. Jeffrey, T. Jeltema, R. Kessler, O. Lahav, J. Lee, S. Lee, C. Lidman, H. Lin, M. Lin, J. L. Marshall, J. Mena-Fernández, R. Miquel, J. Muir, A. Möller, R. C. Nichol, A. Palmese, M. Paterno, W. J. Percival, A. Pieres, A. A. Plazas Malagón, B. Popovic, A. Porredon, J. Prat, H. Qu, M. Raveri, M. Rodriguez-Monroy, A. K. Romer, E. S. Rykoff, M. Sako, S. Samuroff, E. Sanchez, D. Sanchez Cid, D. Scolnic, I. Sevilla-Noarbe, P. Shah, E. Sheldon, M. Smith, E. Suchyta, M. Sullivan, M. E. C. Swanson, B. O. Sánchez, G. Tarle, G. Taylor, D. Thomas, C. To, L. Toribio San Cipriano, M. Toy, M. A. Troxel, D. L. Tucker, V. Vikram, M. Vincenzi, A. R. Walker, N. Weaverdyck, J. Weller, P. Wiseman, M. Yamamoto, B. Yanny

TL;DR

DES final DES BAO and SN data, when combined with external Planck CMB information and priors on the sound horizon, age, and BBN, challenge flat ΛCDM and motivate exploring extensions to curvature and dynamical dark energy. Using four background models (ΛCDM, kΛCDM, wCDM, w0w_aCDM) and a CPL parameterization, the study employs Bayesian inference with CosmoSIS/CAMB and evaluates tensions via parameter-shift and cross-probe metrics. The strongest indication arises in CPL (w0w_aCDM), where BAO+SN+CMB prefers w0>-1 and wa<0, yielding a ~3.2σ deviation from ΛCDM and improved cross-probe consistency; this is complemented by competitive H0 values near Planck's. Neutrino-mass variations tighten bounds but do not resolve tensions, and a cosmographic expansion yields H0 ≈ 68 km s⁻¹ Mpc⁻¹ with modest model-order sensitivity. Overall, the results hint at evolving dark energy, but caution remains due to potential systematics and the need for growth-of-structure probes to test consistency across DES measurements and external data.

Abstract

The Dark Energy Survey (DES) recently released the final results of its two principal probes of the expansion history: Type Ia Supernovae (SNe) and Baryonic Acoustic Oscillations (BAO). We explore the cosmological implications of these data in combination with external Cosmic Microwave Background (CMB), Big Bang Nucleosynthesis (BBN), and age-of-the-Universe information. The BAO measurement, $\sim2σ$ away from Planck's $Λ$CDM predictions, pushes for low values of $Ω_{\rm m}$ compared to Planck, in contrast to SN which prefers a higher value. We identify several tensions among datasets in the $Λ$CDM model that cannot be resolved by including either curvature or a constant dark energy equation of state. By combining BAO+SN+CMB despite these mild tensions, we obtain $Ω_k$=$-5.5^{+4.6}_{-4.2}\times10^{-3}$ in $kΛ$CDM, and $w=-0.948^{+0.028}_{-0.027}$ in $w$CDM. In $w$CDM, BAO and SN push again in different directions of parameter space, favoring, respectively $w<-1$ and $w>-1$. If we open the parameter space to $w_0w_a$CDM, all the datasets are mutually more compatible, and we find concordance in the $w_0>-1,w_a<0$ quadrant, with BAO pushing for $w_a<0$ and SN for $[w_0>-1,w_a<0]$. For DES BAO and SN in combination with Planck-CMB, we find a $3.2σ$ deviation from $Λ$CDM, with $w_0=-0.673^{+0.098}_{-0.097}$, $w_a = -1.37^{+0.51}_{-0.50}$, a Hubble constant of $H_0=67.81^{+0.96}_{-0.86}$km s$^{-1}$Mpc$^{-1}$, and an abundance of matter of $Ω_{\rm m}=0.3109^{+0.0086}_{-0.0099}$. For the combination of all the background cosmological probes considered we still find a deviation of $2.8σ$ from $Λ$CDM in the $w_0-w_a$ plane. Assuming a minimal neutrino mass, this work provides tentative evidence for non-$Λ$CDM physics, which is consistent with recent claims in support of evolving dark energy, or a source of unknown systematics.

Dark Energy Survey: implications for cosmological expansion models from the final DES Baryon Acoustic Oscillation and Supernova data

TL;DR

DES final DES BAO and SN data, when combined with external Planck CMB information and priors on the sound horizon, age, and BBN, challenge flat ΛCDM and motivate exploring extensions to curvature and dynamical dark energy. Using four background models (ΛCDM, kΛCDM, wCDM, w0w_aCDM) and a CPL parameterization, the study employs Bayesian inference with CosmoSIS/CAMB and evaluates tensions via parameter-shift and cross-probe metrics. The strongest indication arises in CPL (w0w_aCDM), where BAO+SN+CMB prefers w0>-1 and wa<0, yielding a ~3.2σ deviation from ΛCDM and improved cross-probe consistency; this is complemented by competitive H0 values near Planck's. Neutrino-mass variations tighten bounds but do not resolve tensions, and a cosmographic expansion yields H0 ≈ 68 km s⁻¹ Mpc⁻¹ with modest model-order sensitivity. Overall, the results hint at evolving dark energy, but caution remains due to potential systematics and the need for growth-of-structure probes to test consistency across DES measurements and external data.

Abstract

The Dark Energy Survey (DES) recently released the final results of its two principal probes of the expansion history: Type Ia Supernovae (SNe) and Baryonic Acoustic Oscillations (BAO). We explore the cosmological implications of these data in combination with external Cosmic Microwave Background (CMB), Big Bang Nucleosynthesis (BBN), and age-of-the-Universe information. The BAO measurement, away from Planck's CDM predictions, pushes for low values of compared to Planck, in contrast to SN which prefers a higher value. We identify several tensions among datasets in the CDM model that cannot be resolved by including either curvature or a constant dark energy equation of state. By combining BAO+SN+CMB despite these mild tensions, we obtain = in CDM, and in CDM. In CDM, BAO and SN push again in different directions of parameter space, favoring, respectively and . If we open the parameter space to CDM, all the datasets are mutually more compatible, and we find concordance in the quadrant, with BAO pushing for and SN for . For DES BAO and SN in combination with Planck-CMB, we find a deviation from CDM, with , , a Hubble constant of km sMpc, and an abundance of matter of . For the combination of all the background cosmological probes considered we still find a deviation of from CDM in the plane. Assuming a minimal neutrino mass, this work provides tentative evidence for non-CDM physics, which is consistent with recent claims in support of evolving dark energy, or a source of unknown systematics.

Paper Structure

This paper contains 32 sections, 31 equations, 13 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Data
  3. DES Y6 BAO
  4. Fiducial BAO: angular BAO in $0.6<z_{\rm ph}\xspace<1.2$ (BAO)
  5. Alternative BAO: individual $\Delta z_{\rm ph}\xspace=0.1$ tomographic bins (BAO-5)
  6. DES-SN5YR (SN)
  7. Planck CMB
  8. Temperature and polarization anisotropy (CMB)
  9. Angular scale of the acoustic peak ($\theta_ \star$)
  10. Comoving scale of the acoustic peak ($r_d$)
  11. Age of the Universe ( $t_{\rm U}$)
  12. Big Bang Nucleosynthesis (BBN)
  13. Direct measurement of the Hubble constant (direct $H_0$)
  14. Methods
  15. Background evolution
  16. ...and 17 more sections

Figures (13)

  • Figure 1: Illustration of the distance-redshift relation from DES compared to the best-fit CMB-$\Lambda$CDM and BAO+SN+CMB-$w_0$$w_a$CDM predictions. We show the (comoving) angular distance $D_M(z)$ from DES BAO results both from our fiducial single-bin measurement (evaluated at an effective redshift of $z_{\rm eff}\xspace=0.85$ by fitting all the data in $0.6<z_{\rm ph}\xspace<1.2$), but also the alternative 5-bin split measurements (with individual bins of $\Delta z_{\rm ph}\xspace=0.1$). In this figure, for BAO, we assume a value of $r_d = 147.46$ Mpc (see \ref{['sec:rd']}). We also show the SN binned results, for which we plot the luminosity distance transformed to angular distance using \ref{['eq:distance_equivalence']} for the 1829 SNe in DES-SN5YR (1635 DES SNe + 194 low-$z$ SNe from external samples). To obtain the SN distances we calibrate the SN absolute magnitude $\mathcal{M}$ such that the residuals with respect to the given cosmology average to zero. This calibration is different by $\delta \mathcal{M} \sim 0.06$ for the two cosmologies and hence we show in the lower panels two residual plots, one with SNe calibrated to CMB-only $\Lambda$CDM (this calibration is also used in the upper panel) and the other calibrated to the best-fit $w_0$$w_a$CDM model for the BAO+SN+CMB data combination. The residual plot shows the percentage difference in $D_M(z)$ compared to the best fit. The 1829 SNe are binned with equal numbers in each bin (with the $D_M$ and $z$ shown being the average weighted by the inverse variance of $D_M$). The $w_0$$w_a$CDM model fits better the $z<0.1$ SNe and the $z\gtrsim0.75$ BAO and SN data. We also include two vertical lines to indicate the redshift of matter-dark energy equality ($z_{\rm eq}$, dashed) and the redshift when acceleration starts ($z_{\rm acc}$, dotted) for each the two models. This figure illustrates in a simplified way how BAO and SN together constrain the expansion history models, however, in our analyses both $\mathcal{M}$ and $r_d$ are varied.
  • Figure 2: $\Lambda$CDM. 68% (darker) and 95% (lighter) credible regions of the posteriors of different probe combinations within $\Lambda$CDM. Tensions between constraints are apparent. They are further discussed in the text and quantified in \ref{['tab:tensions']}. We zoom in to the more constraining combinations (including CMB and BAO+SN+BBN+$\theta_ \star$) in \ref{['fig:lcdm_h_Om']}.
  • Figure 3: $\Lambda$CDM zoom-in of the $H_0\xspace$-$\Omega_{\rm m}$ plane to show the most constraining data combinations. We show the 68% and 95% credible regions of the posteriors. As we describe in \ref{['sec:lcdm']}, BAO (red) and SN (blue) tend to push in different directions of the parameter space when combined with CMB. The background probe combination (purple) is in agreement with the CMB constraints besides coming from the combination of datasets in tension with CMB and/or among them, as discussed in the text.
  • Figure 4: $k\Lambda$CDM. 1 and 2 $\sigma$ contours of the 2D posterior of $\Omega_{\rm m}$ and $\Omega_\Lambda$$\equiv (1-$$\Omega_k$$-$$\Omega_{\rm m}$$)$ in $k\Lambda$CDM. The tension among probes in this model is manifest. BAO+CMB and SN+CMB differ by $\sim3\sigma$ in $\Omega_k$ and the background probe combination (purple) is in tension with the CMB constraints. See \ref{['sec:klcdm']} for discussion.
  • Figure 5: $w$CDM. 1 and 2 $\sigma$ contours of the 2D posterior of $w$-$H_0\xspace$ (left) and $w$-$\Omega_{\rm m}$ (right). BAO and SN still push for different regions of parameter space, $w<-1$ and $w>-1$, respectively. Nevertheless, SN dominates the constraints on $w$. Some tensions among probes are still apparent, as discussed in \ref{['sec:wcdm']}.
  • ...and 8 more figures