Improved Cosmological Parameters Constraints from CMB and H(z) Data

We discuss the cosmological degeneracy between the Hubble parameter H(z), the age of the universe and cosmological parameters describing simple variations from the minimal ΛCDM model. We show that independent determinations of the Hubble parameter H(z) such as those recently obtained from ages of passively evolving galaxies, combined with Cosmic Microwave Background data (WMAP 5years), provides stringent constraints on possible deviations from the ΛCDM model. In particular we find that this data combination constrains at the 68% (95%) c. l. the following parameters: sum of the neutrino masses ∑ mν < 0.5 (1.0) eV, number of relativistic neutrino species Nrel = 4.1 +0.4 −0.9 ( +1.1 −1.5), dark energy equation of state parameter w = −0.95 ± 0.17 (± 0.32), and curvature Ωk = 0.002 ± 0.006 (± 0.014) , in excellent agreement with dataset combinations involving Cosmic Microwave Background, Supernovae and Baryon Acoustic Oscillations. This offers a valuable consistency check for systematic errors.