New constraints on cosmological parameters and neutrino properties using the expansion rate of the Universe to z ∼ 1.75

We have assembled a compilation of observational Hubble parameter measurements estimated with the differential evolution of cosmic chronometers, in the redshift range 0 < z < 1.75. This sample has been used, in combination with CMB data and with the most recent estimate of the Hubble constant H 0, to derive new constraints on several cosmological parameters. The new Hubble parameter data are very useful to break some of the parameter degeneracies present in CMB-only analysis, and to constrain possible deviations from the standard (minimal) flat Lambda CDM model. The H(z) data are especially valuable in constraining Omega(k) and Omega(DE) in models that allow a variation of those parameters, yielding constraints that are competitive with those obtained using Supernovae and/or baryon acoustic oscillations. We also find that our H(z) data 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-rel = 3.45 +/- 0.33 using WMAP 7-years data in combination with South Pole Telescope data and our H(z) determinations (N-rel = 3.71 +/- 0.45 using Atacama Cosmology Telescope data instead of South Pole Telescope). We exclude N-rel > 4 at 95% CL (74% CL) using the same datasets combinations. We also put competitive limits on the sum of neutrino masses, Sigma m(nu) < 0.24 eV at 68% confidence level. These results have been proven to be extremely robust to many possible systematic effects, such as the initial choice of stellar population synthesis model adopted to estimate H(z) and the progenitor-bias.