DESI 2024 VI: cosmological constraints from the measurements of baryon acoustic oscillations

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 ΛCDM cosmological model with a matter density Ωₘ=0.295± 0.015. Paired with a BBN prior and the robustly measured acoustic angular scale from the CMB, DESI requires H₀=(68.52±0.62) km/s/Mpc. In conjunction with CMB anisotropies from Planck and CMB lensing data from Planck and ACT, we find Ωₘ=0.307± 0.005 and H₀=(67.97±0.38) 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 w₀ and wₐ, combinations of DESI with CMB or with SN~Ia individually prefer w₀>-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 Pantheon+, Union3, or DES-SN5YR datasets respectively. For the flat ΛCDM model with the sum of neutrino mass ∑ m_ν free, combining the DESI and CMB data yields an upper limit ∑ m_ν < 0.072 $(0.113)$ eV at 95% confidence for a ∑ m_ν>0 (∑ m_ν>0.059) eV prior. These neutrino-mass constraints are substantially relaxed in models beyond ΛCDM. [Abridged.]