The axis of systematic bias in SN Ia cosmology and implications for DESI 2024 results

Robot-controlled optical fibers will help create 3D map of the cosmos.

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. To mitigate confirmation bias, a blind analysis was implemented to measure the BAO scales. DESI BAO data alone are consistent with the standard flat ΛCDM cosmological model with a matter density Ωm=0.295±0.015. Paired with a baryon density prior from Big Bang Nucleosynthesis and the robustly measured acoustic angular scale from the cosmic microwave background (CMB), DESI requires H 0=(68.52±0.62) km s-1 Mpc-1. In conjunction with CMB anisotropies from Planck and CMB lensing data from Planck and ACT, we find Ωm=0.307± 0.005 and H 0=(67.97±0.38) km s-1 Mpc-1. 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 parametrised by w 0 and wa , combinations of DESI with CMB or with type Ia supernovae (SN Ia) individually prefer w 0 > -1 and wa < 0. This preference is 2.6σ for the DESI+CMB combination, and persists or grows when SN Ia are added in, giving results discrepant with the ΛCDM model at the 2.5σ, 3.5σ or 3.9σ levels for the addition of the Pantheon+, Union3, or DES-SN5YR supernova datasets respectively. For the flat ΛCDM model with the sum of neutrino mass ∑ mν free, combining the DESI and CMB data yields an upper limit ∑ mν < 0.072 (0.113) eV at 95% confidence for a ∑ mν > 0 (∑ mν > 0.059) eV prior. These neutrino-mass constraints are substantially relaxed if the background dynamics are allowed to deviate from flat ΛCDM.

The Dark Energy Spectroscopic Instrument (DESI) collaboration recently released its first year of data (DR1) on baryon acoustic oscillations (BAO) in galaxy, quasar, and Lyman-$\alpha$ forest tracers. When combined with cosmic microwave background (CMB) and Type Ia supernovae (SNIa) data, DESI BAO results suggest potential thawing behaviour in dark energy. Cosmological analyses utilize comoving distances along ($D_\mathrm{ H}$) and perpendicular to ($D_\mathrm{ M}$) the line of sight. Notably, there are $1\sim 2\sigma$ deviations in $D_\mathrm{ M}$ and $D_\mathrm{ H}$ from Planck cosmology values in the luminous red galaxies (LRG) bins LRG1 and LRG2.This study examines the role of LRG1 and LRG2 in diverging DESI 2024 BAO cosmology from Planck cosmology. We use angle-averaged distance $D_\mathrm{ V}$ and the ratio $F_{\rm AP}=D_\mathrm{ M}/D_\mathrm{ H}$, which are more directly related to the measured monopole and quadrupole components of the galaxy power spectrum or correlation function, instead of the officially adopted $D_\mathrm{ M}$ and $D_\mathrm{ H}$. This transformation aims to isolate the influence of monopoles in LRG1 and LRG2 on deviations from $w=-1$. Our findings indicate that removing the $D_\mathrm{ V}$ data point in LRG2 aligns DESI + CMB + SNIa data compilation with $w=-1$ within a $2\sigma$ contour and reduces the $H_0$ discrepancy from the Planck 2018 results from $0.63\sigma$ to $0.31\sigma$. Similarly, excluding the $D_\mathrm{ V}$ data point from LRG1 shifts the $w_0/w_a$ contour toward $w=-1$, although no intersection occurs. This highlights the preference of both LRG1 and LRG2 BAO monopole components for the thawing dark energy model, with LRG2 showing a stronger preference. We provide the $D_\mathrm{ V}$ and $F_{\rm AP}$ data and their covariance alongside this paper.

Baryonic Acoustic Oscillation (BAO) data from the Dark Energy Spectroscopic Instrument (DESI), in combination with Cosmic Microwave Background (CMB) data and Type Ia Supernovae (SN) luminosity distances, suggests a dynamical evolution of the dark energy equation of state with a phantom phase (w < -1) in the past when the so-called w 0 wa parametrization w(a) = w 0 + w a (1-a) is assumed. In this work, we investigate more general dark energy models that also allow a phantom equation of state. We consider three cases: an equation of state with a transition feature, a model-agnostic equation of state with constant values in chosen redshift bins, and a k-essence model. Since the dark energy equation of state is correlated with neutrino masses, we reassess constraints on the neutrino mass sum focusing on the model-agnostic equation of state. We find that the combination of DESI BAO with Planck 2018 CMB data and SN data from Pantheon, Pantheon+, or Union3 is consistent with an oscillatory dark energy equation of state, while a monotonic behavior is preferred by the DESY5 SN data. Performing model comparison techniques, we find that the w 0 wa parametrization remains the simplest dark energy model that can provide a better fit to DESI BAO, CMB, and all SN datasets than ΛCDM. Constraints on the neutrino mass sum assuming dynamical dark energy are relaxed compared to ΛCDM and we show that these constraints are tighter in the model-agnostic case relative to w 0 wa model by 70%–90%.

We perform new measurements of the expansion rate and the sound horizon at the end of the baryon decoupling, and derive constraints on cosmic key parameters in the framework of the ΛCDM model, wCDM model, non-flat ΛCDM model and the phenomenological emergent dark energy (PEDE) model. We keep rd and H0 completely free, and use the recent Dark Energy Spectroscopic Instrument (DESI) Year 1 and Dark Energy Survey (DES) Year 6 BAO measurements in the effective redshift range 0.3&lt;z&lt;2.33, combined with the compressed form of the Pantheon sample of Type Ia supernovae, the latest 34 observational H(z) measurements based on the differential age method, and the recent H0 measurement from SH0ES 2022 as an additional Gaussian prior. Combining BAO data with the observational H(z) measurements, and the Pantheon SNe Ia data, we obtain H0=69.70±1.11 km s−1Mpc−1, rd=147.14±2.56 Mpc in flat ΛCDM model, H0=70.01±1.14 km s−1Mpc−1, rd=146.97±2.45 Mpc in PEDE model. The spatial curvature is Ωk=0.023±0.025, and the dark energy equation of state is w=−1.029±0.051, consistent with a cosmological constant. We apply the Akaike information and the Bayesian information criterion test to compare the four models, and see that the PEDE model performs better.

The recent results from the first-year baryon acoustic oscillations (BAO) data released by the Dark Energy Spectroscopic Instrument (DESI), combined with cosmic microwave background (CMB) and Type Ia supernova (SN) data, have shown a detection of significant deviation from a cosmological constant for dark energy. In this work, we utilize the latest DESI BAO data in combination with the SN data from the full 5 yr observations of the Dark Energy Survey and the CMB data from the Planck satellite to explore potential interactions between dark energy and dark matter. We consider four typical forms of the interaction term Q. Our findings suggest that interacting dark energy (IDE) models with Q ∝ ρ de support the presence of an interaction where dark energy decays into dark matter. Specifically, the deviation from ΛCDM for the IDE model with Q = β H 0 ρ de reaches the 3σ level. These models yield a lower value of Akaike information criterion than the ΛCDM model, indicating a preference for these IDE models based on the current observational data. For IDE models with Q ∝ ρ c, the existence of interaction depends on the form of the proportionality coefficient Γ. The IDE model with Q = β H ρ c yields β = 0.0003 ± 0.0011, which essentially does not support the presence of the interaction. In general, whether the observational data support the existence of interaction is closely related to the model. Our analysis helps to elucidate which type of IDE model can better explain the current observational data.

New insights from the Dark Energy Spectroscopic Instrument (DESI) 2024 baryon acoustic oscillations (BAO) data, in conjunction with cosmic microwave background (CMB) and Type Ia supernova (SN) data, suggest that dark energy may not be a cosmological constant. In this work, we investigate the cosmological implications of holographic dark energy (HDE) and interacting holographic dark energy (IHDE) models, utilizing CMB, DESI BAO, and SN data. By considering the combined DESI BAO and SN data, we determine that in the IHDE model, the parameter c>1 1$$\\end{document}]]> and the dark-energy equation of state w does not cross -1 at the 1σ confidence level, whereas in the HDE model, it marginally falls below this threshold. Upon incorporating CMB data, we observe that in the HDE model, the parameter c<1 and w crosses -1 at a level beyond 10σ. Conversely, for the IHDE model, the likelihood of w crossing -1 is considerably diminished, implying that the introduction of interaction within the HDE model could potentially resolve or mitigate the cosmic big rip conundrum. Furthermore, our analysis reveals that the HDE and IHDE models are statistically as viable as the ΛCDM model when assessing Bayesian evidence with DESI BAO data combined with SN data. However, when CMB data are added, the HDE and IHDE models are significantly less favored than the ΛCDM model. Our findings advocate for further exploration of the HDE and IHDE models using forthcoming, more precise late-universe observations.

The sum of neutrino masses can be measured cosmologically, as the sub-eV particles behave as “hot” dark matter whose main effect is to suppress the clustering of matter compared to a universe with the same amount of purely cold dark matter. Current astronomical data provide an upper limit on ∑mν between 0.07–0.12 eV at 95% confidence, depending on the choice of data. This bound assumes that the cosmological model is Λ Cold Dark Matter (ΛCDM), where dark energy is a cosmological constant, the spatial geometry is flat, and the primordial fluctuations follow a pure power law. Here, we update studies on how the mass limit degrades if we relax these assumptions. To existing data from the satellite we add new gravitational lensing data from the Atacama Cosmology Telescope, the new Type Ia supernova sample from the Pantheon+survey, and baryonic acoustic oscillation (BAO) measurements from the Sloan Digital Sky Survey and the Dark Energy Spectroscopic Instrument. Using our fiducial data combination, described in the appendix, we find the neutrino mass limit is stable to most model extensions, with such extensions degrading the limit by less than 10%. We find a broadest bound of ∑mν&lt;0.19 eV at 95% confidence for a model with dynamical dark energy, although this scenario is not statistically preferred over the simpler ΛCDM model.

We present the first cosmological parameter constraints using measurements of type Ia supernovae (SNe Ia) from the Dark Energy Survey Supernova Program (DES-SN). The analysis uses a subsample of 207 spectroscopically confirmed SNe Ia from the first three years of DES-SN, combined with a low-redshift sample of 122 SNe from the literature. Our “DES-SN3YR” result from these 329 SNe Ia is based on a series of companion analyses and improvements covering SN Ia discovery, spectroscopic selection, photometry, calibration, distance bias corrections, and evaluation of systematic uncertainties. For a flat ΛCDM model we find a matter density . For a flat wCDM model, and combining our SN Ia constraints with those from the cosmic microwave background (CMB), we find a dark energy equation of state , and . For a flat w 0 w a CDM model, and combining probes from SN Ia, CMB and baryon acoustic oscillations, we find and . These results are in agreement with a cosmological constant and with previous constraints using SNe Ia (Pantheon, JLA).

The latest baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) Collaboration, when combined with Planck satellite cosmic microwave background (CMB) data and type Ia supernovae, suggest a preference for dynamical dark energy (DDE) at a significance level ranging from 2.8σ to 4.2σ. In this work, I test whether, and to what extent, this preference is supported by CMB experiments other than Planck. I analyze the latest Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT) temperature, polarization, and lensing spectra at small scales, eventually combining them with Planck or Wilkinson microwave anisotropy probe (WMAP) 9-yr observations at large angular scales. My analysis shows that ACT and WMAP data, when combined with DESI BAO and Pantheon+ supernovae, yield independent constraints with a precision comparable to Planck. Notably, in this case, the cosmological constant value is recovered within 2 standard deviations. A preference for DDE reappears when Pantheon+ is replaced with distance moduli measurements from the Dark Energy Survey supernova program (DESy5). However, it remains less pronounced compared to the Planck-based results. When considering SPT data, no clear preference for DDE is found in combinations involving Pantheon+ supernovae, and the preference is significantly weaker in combinations involving DESy5. Overall, CMB experiments other than Planck generally weaken the evidence for DDE. I argue that the subsets of Planck data that strengthen the shift toward DDE are the temperature and E-mode polarization anisotropy measurements at large angular scales ℓ≲30.

Possible interaction between dark energy and dark matter has previously shown promise in alleviating the clustering tension, without exacerbating the Hubble tension, when Baryon Acoustic Oscillations (BAO) data from the Sloan Digital Sky Survey (SDSS) DR16 is combined with Cosmic Microwave Background (CMB) and Type-Ia Supernovae (SNIa) data sets. With the recent Dark Energy Spectroscopic Instrument (DESI) BAO DR2, there is now a compelling need to re-evaluate this scenario. We combine DESI DR2 with Planck 2018 and Pantheon + SNIa data sets to constrain interacting dark matter dark energy models, accounting for interaction effects in both the background and perturbation sectors. Our results exhibit similar trends to those observed with SDSS, albeit with improved precision, reinforcing the consistency between the two BAO data sets. In addition to offering a resolution to the $S_8$ tension, in the phantom-limit, the dark energy equation of state exhibits an early-phantom behaviour, aligning with DESI DR2 findings, before transitioning to $w\sim -1$ at lower redshifts, regardless of the DE parametrization. However, the statistical significance of excluding $w=-1$ is reduced compared to their non-interacting counterparts.

We investigate a new type of dark energy model called the generalized emergent dark energy (GEDE) model which encodes either phenomenologically emergent dark energy that has no effective presence in the early times and emerges strongly in late times or the standard model of cosmology Lambda cold dark matter ($\Lambda$CDM). We test this new brand dark energy model and compare it with the standard model of cosmology $\Lambda$CDM using the final baryon acoustic oscillation (BAO) uncorrelated measurements in the effective redshift range $0.106 \le z \le 2.33$ of different surveys after two decades of dedicated spectroscopic observation combined with the compressed form of the Pantheon sample of Type Ia supernovae, the observational $H(z)$ measurements based on differential age method, and the recent Hubble constant value measurement from the Hubble Space Telescope and the SH0ES Team in 2022 as an additional Gaussian prior. In the GEDE model fit yields the cosmological parameters $\Omega _{m}=0.2713 \pm 0.0142$ and $\Omega _{\Lambda }=0.7245 \pm 0.0126$ for BAO + R22. Combining BAO with the observational $H(z)$ measurements based on the differential age method, and the Pantheon Type Ia supernova, the Hubble constant yields 69.92 $\pm$ 1.17 km s$^{-1}$ Mpc$^{-1}$ and the sound horizon gives 145.97 $\pm$ 2.44 Mpc. We perform the Akaike information criteria, Bayesian information criterion, and Bayesian evidence to compare the GEDE and $\Lambda$CDM models and see that $\Lambda$CDM has a better performance without the inclusion of early-time observations as the cosmic microwave background.

Relieve the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e2446" altimg="si172.svg"><mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msub></mml:math> tension with a new coupled generalized three-form dark energy model

The Dark Energy Spectroscopic Instrument (DESI) will provide precise measurements of Baryon Acoustic Oscillations (BAO) to constrain the expansion history of the Universe and set stringent constraints on dark energy. Therefore, precise control of the global error budget due to various systematic effects is required for the DESI 2024 BAO analysis. In this work, we estimate the level of systematics induced in the DESI BAO analysis due the assumed Halo Occupation Distribution (HOD) model for the Emission Line Galaxy (ELG) tracer. We make use of mock galaxy catalogs constructed by fitting various HOD models to early DESI data, namely the One-Percent survey data. Our analysis includes typical HOD models for the ELG tracer used in the literature as well as extensions to the baseline models. Among the extensions, we consider various recipes for galactic conformity and assembly bias. We use 25 AbacusSummit simulations under the ΛCDM cosmology for each HOD model and perform independent analyses in Fourier space and in configuration space. To recover the BAO signal from our mocks we perform BAO reconstruction and apply the control variates technique to reduce sample variance noise. Our BAO analyses can recover the isotropic BAO parameter α iso within 0.1% and the Alcock Paczynski parameter α AP within 0.3%. Overall, we find that the systematic error due to the HOD dependence is below 0.17%, with the Fourier space analysis being more robust against the HOD systematics. We conclude that our analysis pipeline is robust enough against the HOD systematics for the ELG tracer in the DESI 2024 BAO analysis, for the assumptions made.

Holographic dark energy (HDE), which arises from a theoretical attempt to apply the holographic principle (HP) to the dark energy (DE) problem, has attracted significant attention over the past two decades. We perform a comprehensive numerical study on HDE models that can be classified into four categories: 1) HDE models with other characteristic length scale, 2) HDE models with extended Hubble scale, 3) HDE models with dark sector interaction, 4) HDE models with modified black hole entropy. For theoretical models, we select seven representative models, including the original HDE (OHDE) model, Ricci HDE (RDE) model, generalized Ricci HDE (GRDE) model, interacting HDE (IHDE1 and IHDE2) models, Tsallis HDE (THDE) model, and Barrow HDE (BHDE) model. For cosmological data, we use the Baryon Acoustic Oscillation (BAO) data from the Dark Energy Spectroscopic Instrument (DESI) 2024 measurements, the Cosmic Microwave Background (CMB) distance priors data from the Planck 2018, and the type Ia supernovae (SNe) data from the PantheonPlus compilation. Using χ2tatistic and Bayesian evidence, we compare these HDE models with current observational data. It is found that: 1) The ΛCDM remains the most competitive model, while the RDE model is ruled out. 2) HDE models with dark sector interaction perform the worst across the four categories, indicating that the interaction term is not favored under the framework of HDE. 3) The other three categories show comparable performance. The OHDE model performs better in the BAO+CMB dataset, and the HDE models with modified black hole entropy perform better in the BAO+CMB+SN dataset. 4) HDE models with the future event horizon exhibit significant discrepancies in parameter space across datasets. The BAO+CMB dataset favors a phantom-like HDE, whereas the BAO+CMB+SN leads to an equation of state (EoS) much closer to the cosmological constant.