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 \pm 0.33 using WMAP 7-years data in combination with South Pole Telescope data and our H ( z ) determinations ( N _ { rel } = 3.71 \pm 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 .