First Cosmological Constraints on Dark Energy from the Radial Baryon Acoustic Scale

We present cosmological constraints arising from the first measurement of the radial (line-of-sight) baryon acoustic oscillations (BAO) scale in the large scale structure traced by the galaxy distribution. Here we use these radial BAO measurements at z=0.24 and z=0.43 to derive new constraints on dark energy and its equation of state for a flat universe, without any other assumptions on the cosmological model: w=-1.14±0.39 (assumed constant), Ω_m=0.24_-0.05^+0.06. If we drop the assumption of flatness and include previous cosmic microwave background and supernova data, we find w=-0.974±0.058, Ω_m=0.271±0.015, and Ω_k=-0.002±0.006, in good agreement with a flat cold dark matter cosmology with a cosmological constant. To our knowledge, these are the most stringent constraints on these parameters to date under our stated assumptions.