Constraining the time evolution of dark energy, curvature and neutrino properties with cosmic chronometers
Abstract
We use the latest compilation of observational Hubble parameter measurements estimated with the differential evolution of cosmic chronometers, in the redshift range 0<z<2, to place constraints on cosmological parameters. We used a MarkovChain MonteCarlo approach to sample the parameter space for the cosmic chronometers dataset alone and in combination with other stateofthe art cosmological measurements: CMB data from the latest Planck 2015 release, the most recent estimate of the Hubble constant H_{0}, a compilation of recent baryon acoustic oscillation data, and the latest type Ia cosmological supernovae sample. From lateUniverse probes alone (z<2) we find that w_{0} = 0.9 ± 0.18 and w_{a} = 0.5 ± 1.7, and when combining also Planck 2015 data we obtain w_{0}=0.98± 0.11 and w_{a}=0.30±0.4. These new constraints imply that nearly all quintessence models are disfavoured by the data; only phantom models or a pure cosmological constant are favoured. This is a remarkable finding as it imposes severe constraints on the nature of dark energy. For the curvature our constraints are Ω_{k} = 0.003 ± 0.003, considering also CMB data. We also find that H(z) data from cosmic chronometers are important to constrain parameters that do no affect directly the expansion history, by breaking or reducing degeneracies with other parameters. We find that N_{eff} = 3.17 ± 0.15, thus excluding the possibility of an extra (sterile) neutrino at more than 5 σ, and put competitive limits on the sum of neutrino masses, Σ m_{ν}< 0.27 eV at 95% confidence level. Finally, we constrain the redshift evolution of dark energy by exploring separately the early and lateUniverse, and find a dark energy equation of state evolution w(z) consistent with that in the ΛCDM model at the ± 0.4 level over the entire redshift range 0 < z < 2.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 December 2016
 DOI:
 10.1088/14757516/2016/12/039
 arXiv:
 arXiv:1604.00183
 Bibcode:
 2016JCAP...12..039M
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 19 pages, 9 figures, 6 tables, submitted to JCAP. The cosmic chronometers data used in this analysis can be downloaded at http://www.physicsastronomy.unibo.it/en/research/areas/astrophysics/cosmologywithcosmicchronometers