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

Abstract
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.