Reionization optical depth and CMB-BAO tension in punctuated inflation

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.

We introduce a new diagnostic for the null tests of dynamical dark energy alongside two other combined equivalent diagnostics. These diagnostics are useful, especially when we include anisotropic baryon acoustic oscillation (BAO) data in an analysis, to quantify the deviations from the standard ΛCDM model. We also consider another diagnostic for isotropic BAO observations. These null tests are independent of any late-time dark energy model or parametrization. With these diagnostics, we study the evidence for dynamical dark energy in light of Dark Energy Spectroscopic Instrument (DESI) 2024 data combined with cosmic microwave background (CMB) observations of the Planck 2018 mission and local H 0 measurements. We find no strong evidence for dynamical dark energy. The exclusion of the individual deviations at the effective redshift 0.51 of the DESI 2024 data makes the evidence even weaker. We get nearly similar results for other non-DESI BAO data. Both for DESI 2024 and other non-DESI BAO data, the evidence is almost independent of early-time physics. The evidence corresponding to the SHOES value of H 0 is higher than the corresponding tRGB value of H 0 for all combinations of data, but still not strong enough to reject the flat ΛCDM model.

In light of the evidence for dynamical dark energy (DE) found from the most recent Dark Energy Spectroscopic Instrument (DESI) baryon acoustic oscillation (BAO) measurements, we perform a nonparametric, model-independent reconstruction of the DE density evolution. To do so, we develop and validate a new framework that reconstructs the DE density through a third-degree piecewise polynomial interpolation, allowing for direct constraints on its redshift evolution without assuming any specific functional form. The strength of our approach resides in the choice of directly reconstructing the DE density, which provides a more straightforward relation to the distances measured by BAO than the equation of state parameter. We investigate the constraining power of cosmic microwave background (CMB) observations combined with supernovae (SNe) and BAO measurements. In agreement with results from other works, we find a preference for deviations from ΛCDM, with a significance of 2.4σ when using the Dark Energy Survey Year 5 (DESY5) SNe data, and 1.3σ with PantheonPlus. In all the cases we consider, the derived DE equation of state parameter presents evidence for phantom crossing. By investigating potential systematic effects in the low-redshift samples of DESY5 observations, we confirm that correcting for the offset in apparent magnitude with respect to PantheonPlus data, as suggested in previous studies, completely removes the tension. Furthermore, we assess the risk of potentially overfitting the data by changing the number of interpolation nodes. As expected, we find that with lesser nodes we get a smoother reconstructed behavior of the DE density, although with similar overall features. The pipeline developed in this work is ready to be used with future high-precision data to further investigate the evidence for a nonstandard background evolution.

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

Baryon acoustic oscillation measurements by the Dark Energy Spectroscopic Instrument (Data Release 1) have revealed exciting results that show evidence for dynamical dark energy at ∼ 3σ when combined with cosmic microwave background and type Ia supernova observations. These measurements are based on the w 0 w a CDM model of dark energy. The evidence is less in other dark energy models such as the wCDM model. In order to avoid imposing a dark energy model, we reconstruct the distance measures and the equation of the state of dark energy independent of any dark energy model and driven only by observational data. Our results show that the model-agnostic (in terms of late-time models) evidence for dynamical dark energy from DESI is not significant. Our analysis also provides model-independent constraints on cosmological parameters such as the Hubble constant and the matter-energy density parameter at present. Although we used CMB distance priors (not full CMB data) from a ΛCDM early-time model, our results remain largely similar for other cosmological models, provided that these models do not differ significantly from the standard model.

Recent measurements of baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI) show hints of tension with data from the cosmic microwave background (CMB) when interpreted within the standard model of cosmology. In this short note we discuss the consequences of one solution to this tension, a small but negative spatial curvature with R k = 21 H 0 -1, which DESI measures at 2σ when combined with CMB data. We describe the physical role of curvature in cosmological distance measures tied to recombination, i.e. the CMB and BAO, and the relation to neutrino mass constraints which are relaxed to ∑ mν < 0.10 eV at 95% confidence when curvature is allowed to deviate from zero. A robust detection of negative curvature would have significant implications for inflationary models: improved BAO measurements, particularly from future high-redshift spectroscopic surveys, will be able to distinguish curvature from other solutions to the DESI-CMB tension like phantom dark energy at high significance.

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%.

The Dark Energy Spectroscopic Instrument (DESI) Collaboration has obtained robust measurements of baryon acoustic oscillations in the redshift range 0.1&lt;z&lt;4.2, based on the Lyman-α forest and galaxies from data release 2. We combine these measurements with cosmic microwave background (CMB) data from and the Atacama Cosmology Telescope to place our tightest constraints yet on the sum of neutrino masses. Assuming the cosmological ΛCDM model and three degenerate neutrino states, we find ∑mν&lt;0.0642 eV (95%) with a marginalized error of σ(∑mν)=0.020 eV. We also constrain the effective number of neutrino species, finding Neff=3.23−0.34+0.35 (95%), in line with the Standard Model prediction. When accounting for neutrino oscillation constraints, we find a preference for the normal mass ordering and an upper limit on the lightest neutrino mass of ml&lt;0.023 eV (95%). However, we determine using frequentist and Bayesian methods that our constraints are in tension with the lower limits derived from neutrino oscillations. Correcting for the physical boundary at zero mass, we report a 95% Feldman-Cousins upper limit of ∑mν&lt;0.053 eV, breaching the lower limit from neutrino oscillations. Considering a more general Bayesian analysis with an effective cosmological neutrino mass parameter, ∑mν,eff, that allows for negative energy densities and removes unsatisfactory prior weight effects, we derive constraints that are in 3σ tension with the same oscillation limit, while the error rises to σ(∑mν,eff)=0.053 eV. In the absence of unknown systematics, this finding could be interpreted as a hint of new physics not necessarily related to neutrinos. The preference of DESI and CMB data for an evolving dark energy model offers one possible solution. In the w0waCDM model, we find ∑mν&lt;0.163 eV (95%), relaxing the neutrino tension. These constraints all rely on the effects of neutrinos on the cosmic expansion history. Using full-shape power spectrum measurements of data release 1 galaxies, we place complementary constraints that rely on neutrino free streaming. Our strongest such limit in ΛCDM, using selected CMB priors, is ∑mν&lt;0.193 eV (95%).

To elucidate the robustness of the baryon acoustic oscillation (BAO) data measured by the dark energy spectroscopic instrument (DESI) in capturing the dynamical behavior of dark energy, we assess the model dependence of the evidence for dynamical dark energy inferred from the DESI BAO data. While the DESI BAO data slightly tightens the constraints on model parameters and increases the tension between the Chevallier–Polarski–Linder (CPL) model and the ΛCDM model, we find that the influence of DESI BAO data on the constraint of w0 is small in the SSLCPL model. In comparison to the CPL model, the tension with the ΛCDM model is reduced for the SSLCPL model, suggesting that the evidence for dynamical dark energy from DESI BAO data is dependent on cosmological models. The inclusion of spatial curvature has little impact on the results in the SSLCPL model.

The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), when combined with data from the cosmic microwave background (CMB), has placed an upper-limit on the sum of neutrino masses, ∑mν< 70 meV (95%). In addition to excluding the minimum sum associated with the inverted hierarchy, the posterior is peaked at ∑mν = 0 and is close to excluding even the minumum sum, 58 meV at 2σ. In this paper, we explore the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined in cosmology from the suppression of clustering in the late universe. Allowing the clustering to be enhanced, we extended the DESI analysis to ∑mν< 0 and find ∑mν =160±90 meV (68%), and that the suppression of power from the minimum sum of neutrino masses is excluded at 99% confidence. We show this preference for negative masses makes it challenging to explain the result by a shift of cosmic parameters, such as the optical depth or matter density. We then show how a result of ∑mν = 0 could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics that is accessible in a wide range of experiments. In addition, we discuss how an apparent signal with ∑mν< 0 can arise from new long range forces in the dark sector or from a primordial trispectrum that resembles the signal of CMB lensing.

Recent observations of baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI) survey, when combined with measurements of the cosmic microwave background (CMB) and Type Ia supernovae (SNIa), provide compelling evidence for a phantom crossing at late times, along with statistically significant deviations from the standard ΛCDM model. In this work, we investigate the role of redshift-space galaxy clustering data by employing the pre-reconstruction full-shape (FS) galaxy power spectrum from the Baryon Oscillation Spectroscopic Survey (BOSS) data release 12 (DR12) sample. This dataset is analyzed in combination with BAO measurements from DESI data release 2 (DR2) and various SNIa samples. Our analysis demonstrates that the joint combination of these datasets can yield deviations from ΛCDM at a significance level of up to ∼ 5σ, suggesting strong indications that the dark energy equation of state parameter w(z) may have crossed the phantom divide (w = -1) in the redshift range z ∼ 0.4–0.5. The precise location and strength of this crossing depend on the adopted theoretical parameterizations. Importantly, our results reveal that this trend persists even in the absence of CMB data, underscoring the robustness of the FS power spectrum as a powerful and independent probe for testing dark energy models and for distinguishing between competing cosmological scenarios.

The Dark Energy Spectroscopic Instrument (DESI) collaboration, combining their baryon acoustic oscillation (BAO) data with cosmic microwave background (CMB) anisotropy and supernovae data, have found significant indication against the Lambda cold dark matter ($\Lambda$CDM) cosmology. This can also be interpreted as the significance of the detection of the $w_a$ parameter that measures variation of the dark energy equation of state. DESI’s DR2 article quotes exclusion of $\Lambda$CDM for combinations of BAO and CMB data with each of three different and overlapping supernovae compilations (at 2.8σ for Pantheon+ , 3.8σ for Union3, and 4.2σ for DESY5). We show that one can neither choose amongst nor average over these three different significances. We demonstrate how a principled statistical combination yields a combined exclusion significance of 3.1σ. Further we argue that, faced with these competing significances, the most secure inference from the DESI DR2 results is the 3.1σ level exclusion of $\Lambda$CDM obtained from combining DESI + CMB alone, omitting supernovae.

We investigate constraints on the Hubble constant (H0) using Baryon Acoustic Oscillations (BAO) and baryon density measurements from Big Bang Nucleosynthesis (BBN). We start by investigating the tension between galaxy BAO measurements and those using the Lyman-α forest, within a Bayesian framework. Using the latest results from eBOSS DR14 we find that the probability of this tension being statistical is ≃6.3% assuming flat ΛCDM. We measure H0 = 67.6±1.1 km s−1 Mpc−1, with a weak dependence on the BBN prior used, in agreement with results from Planck Cosmic Microwave Background (CMB) results and in strong tension with distance ladder results. Finally, we forecast the future of BAO + BBN measurements of H0, using the Dark Energy Spectroscopic Instrument (DESI). We find that the choice of BBN prior will have a significant impact when considering future BAO measurements from DESI.

Recent baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) collaboration, combined with the cosmic microwave background (CMB) and type Ia supernovae observations, suggest a preference for dynamical dark energy (DDE) with w 0 &gt; −1 and w a &lt; 0. Given the cosmological origin of fast radio bursts (FRBs), the combination of their dispersion measures (DMs) and host galaxy redshifts makes localized FRBs a valuable tool for probing cosmology. Using an updated sample of 92 localized FRBs, along with DESI BAO, PlantheonPlus, and CMB data, we constrain the dark energy (DE) equation of state (EoS) under the Chevallier–Polarski–Linder parameterization. We find that even without incorporating CMB data, DDE remains preferred with w 0 = − 0.85 5 − 0.084 + 0.084 and w a = − 1.17 4 − 0.491 + 0.462 at a confidence level of ∼2.5σ. A joint analysis constrains these to be w 0 = − 0.78 4 − 0.064 + 0.064 and w a = − 0.87 2 − 0.278 + 0.269 , showing a discrepancy with ΛCDM at a ∼3.1σ level. Furthermore, using localized FRBs alone, we estimate the Hubble constant H 0 to be 69.0 4 − 2.07 + 2.30 and 75.6 1 − 2.07 + 2.23 km s − 1 Mpc − 1 , assuming the Galactic electron density models to be NE2001 and YMW16, respectively. Thus, accurate accounting of the Galactic DM is crucial for resolving the Hubble tension with FRBs. Future BAO measurements, next-generation CMB experiments, and more localized FRBs will further constrain the DE EoS and the cosmological parameters.

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.