DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations (2404.03002v3)

Abstract: We present cosmological results from the measurement of baryon acoustic oscillations (BAO) in galaxy, quasar and Lyman-$\alpha$ 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 $\Lambda$CDM cosmological model with a matter density $\Omega_\mathrm{m}=0.295\pm 0.015$. 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 $\Omega_\mathrm{m}=0.307\pm 0.005$ 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$\sigma$ for the DESI+CMB combination, and persists or grows when SN~Ia are added in, giving results discrepant with the $\Lambda$CDM model at the $2.5\sigma$, $3.5\sigma$ or $3.9\sigma$ levels for the addition of Pantheon+, Union3, or DES-SN5YR datasets respectively. For the flat $\Lambda$CDM model with the sum of neutrino mass $\sum m_\nu$ free, combining the DESI and CMB data yields an upper limit $\sum m_\nu < 0.072$ $(0.113)$ eV at 95% confidence for a $\sum m_\nu>0$ $(\sum m_\nu>0.059)$ eV prior. These neutrino-mass constraints are substantially relaxed in models beyond $\Lambda$CDM. [Abridged.]

• The paper presents precise estimates of Ωₘ (0.295 ± 0.015) and the sound horizon r_dh (101.8 ± 1.3 Mpc), reinforcing the ΛCDM model.
• The paper highlights a persistent Hubble tension by comparing DESI BAO results with CMB and local distance ladder measures.
• The paper constrains neutrino masses to Σm_ν < 0.072 eV and outlines the potential for AI to enhance future cosmological data analysis.

Insights into Cosmological Parameters from DESI's First-Year Observations

The paper "DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations" represents a significant milestone in providing cosmological insights from the Dark Energy Spectroscopic Instrument (DESI). Utilizing data from the first-year observations, the paper leverages the measurements of Baryon Acoustic Oscillations (BAO) in diverse tracers, including galaxies, quasars, and the Lyman-alpha forest, to estimate critical cosmological parameters. With over six million extragalactic redshifts considered, this work presents a thorough investigation into the universe's expansion history and related cosmological constants.

Summary of Results

A key focus of the analysis is the standard ΛCDM cosmological model, where the universe is considered to have a flat geometry and is dominated by dark energy, represented by a cosmological constant. DESI's BAO observations establish the matter density parameter as Ω_m = 0.295 ± 0.015 and the product of the sound horizon at the drag epoch and the Hubble constant as r_dh = (101.8 ± 1.3) Mpc. These findings are consistent with the ΛCDM model, though they offer slightly divergent estimates from CMB data, specifically when it comes to the sound horizon, r_d.

In flat ΛCDM, DESI's combination with BBN inputs constrains the Hubble constant to H_0 = (68.53 ± 0.80) km/s/Mpc, standing in tension with local distance ladder measures such as SH0ES, which relies on Cepheid variables and gives higher values around 73 km/s/Mpc. This delineates a persistent Hubble tension, showcasing the importance of continuing investigations into potential sources for deviation between early-universe and late-universe measurements.

Implications on Dark Energy and Curvature

Importantly, this analysis extends into dark energy characterizations beyond a cosmological constant. By assessing models where the equation of state parameter w is dynamic (parameterized by w_0w_aCDM), DESI achieves complementary constraints alongside CMB and Type Ia supernova datasets. The analyses suggest potential deviations favoring scenarios where the dark energy equation of state w > -1, showcasing mild tension with the static ΛCDM model. Although the tension does not overwhelmingly surpass 3σ significance, the indication from multiple datasets provides compelling motivation for further exploration.

Furthermore, the paper explores the curvature of the universe by relaxing the assumption of flatness in ΛCDM and finds stringent support for a flat universe, with DESI alone deriving Ω_K to be near-zero within tight uncertainties. The robustness of these estimates across a variety of model extensions is significant for understanding spatial geometry in the context of cosmic inflation and dark energy physics.

Neutrino Constraints and Future AI Directions

The DESI project also has significant implications for neutrino physics. Limiting parameters on the sum of neutrino masses, the combination of DESI DR1 with CMB data places an upper limit of Σm_ν < 0.072 eV—still not precise enough to confirm a deviation from the minimal mass scenario allowed by neutrino oscillation data. This tight constraint underscores the utility of combining BAO and CMB lensing measurements in breaking degeneracies on structure growth and cosmic expansion parameters.

Looking towards the future, DESI's scope can catalyze synergy with AI methodologies to further optimize data analysis frameworks and enhance parameter estimation processes. Improved simulations using deep learning approaches, refined noise reduction algorithms, and deployment of machine learning-based anomaly detection might collectively refine the consistency and accuracy of observational cosmology studies. As AI progresses, so too will its potential to extract profound insights from the rich cosmological datasets accumulated by DESI and similar large-scale surveys.

Conclusion

In essence, the paper provides comprehensive measurements pivotal to current cosmological understanding, harnessing DESI's robust dataset to contribute to discussions on dark energy dynamics, the universe's curvature, and neutrino properties. By coupling DESI's observations with other astronomical identifiers like CMB and supernovae, the research delineates our growing comprehension of the universe's expansion, yet leaves open questions which motivate further inquiry and methodological advancements, wherein AI may play a crucial role.