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 Ω_{m}=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