We derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation ( BAO ) measurements with cosmic microwave background ( CMB ) data and a recent reanalysis of Type Ia supernova ( SN ) data .
In particular , we take advantage of high-precision BAO measurements from galaxy clustering and the Lyman- \alpha forest ( LyaF ) in the SDSS-III Baryon Oscillation Spectroscopic Survey ( BOSS ) .
Treating the BAO scale as an uncalibrated standard ruler , BAO data alone yield a high confidence detection of dark energy ; in combination with the CMB angular acoustic scale they further imply a nearly flat universe .
Adding the CMB-calibrated physical scale of the sound horizon , the combination of BAO and SN data into an “ inverse distance ladder ” yields a measurement of H _ { 0 } = 67.3 \pm 1.1 { km } { s } ^ { -1 } { Mpc } ^ { -1 } , with 1.7 % precision .
This measurement assumes standard pre-recombination physics but is insensitive to assumptions about dark energy or space curvature , so agreement with CMB-based estimates that assume a flat \Lambda CDM cosmology is an important corroboration of this minimal cosmological model .
For constant dark energy ( \Lambda ) , our BAO+SN+CMB combination yields matter density \Omega _ { m } = 0.301 \pm 0.008 and curvature \Omega _ { k } = -0.003 \pm 0.003 .
When we allow more general forms of evolving dark energy , the BAO+SN+CMB parameter constraints are always consistent with flat \Lambda CDM values at \approx 1 \sigma .
While the overall \chi ^ { 2 } of model fits is satisfactory , the LyaF BAO measurements are in moderate ( 2 - 2.5 \sigma ) tension with model predictions .
Models with early dark energy that tracks the dominant energy component at high redshift remain consistent with our expansion history constraints , and they yield a higher H _ { 0 } and lower matter clustering amplitude , improving agreement with some low redshift observations .
Expansion history alone yields an upper limit on the summed mass of neutrino species , \sum m _ { \nu } < 0.56 { eV } ( 95 % confidence ) , improving to \sum m _ { \nu } < 0.25 { eV } if we include the lensing signal in the Planck CMB power spectrum .
In a flat \Lambda CDM model that allows extra relativistic species , our data combination yields N _ { eff } = 3.43 \pm 0.26 ; while the LyaF BAO data prefer higher N _ { eff } when excluding galaxy BAO , the galaxy BAO alone favor N _ { eff } \approx 3 .
When structure growth is extrapolated forward from the CMB to low redshift , standard dark energy models constrained by our data predict a level of matter clustering that is high compared to most , but not all , observational estimates .