Constraints on the cosmic expansion rate at redshift 2.3 from the Lyman-α forest

We determine the product of the expansion rate and angular-diameter distance at redshift z=2.3 from the anisotropy of Lyman-α (Lyα) forest correlations measured by the Sloan Digital Sky Survey (SDSS). Our result is the most precise from large-scale structure at z>1. Using the flat Λ cold dark matter model we determine the matter density to be ωm=0.36-0.04+0.03 from Lyα alone. This is a factor of 2 tighter than baryon acoustic oscillation results from the same data due to our use of a wide range of scales (25<r<180 h-1 Mpc). Using a nucleosynthesis prior, we measure the Hubble constant to be H0=63.2±2.5 km/s/Mpc. In combination with other SDSS tracers, we find H0=67.2±0.9 km/s/Mpc and measure the dark energy equation-of-state parameter to be w=-0.90±0.12. Our Letter opens a new avenue for constraining cosmology at high redshift.