Direct constraint on cosmic neutrino mass using observational Hubble parameter data

In order to explore the properties of cosmic neutrinos, i.e. sum of the neutrino mass （∑mv） and the effective number of neutrino species （Neff）, which affects the Hubble expansion rate H（z） and the power of observational Hubble parameter data （OHD） in constraining cosmological parameters under the ACDM model, we utilize OHD to constrain the properties of cosmic neutrinos and apply an accurate H（z） function with ∑ mv, and Neff. First, we simulate new OHD beyond the existing 43 OHD. According to the predictions of measurements of Ho （the current H（z） value）, baryon acoustic oscillations （BAO） peaks, Sandage-Loeb （SL） test and cosmic microwave background （CMB）, we as-sume observational accuracy up to 2% and redshift 0 〈 z ~〈 5. With simulated H（z） data obtained from the fiducial model, we constrain the parameters including ∑ mv, and Neff. When all parameters are set free, ∑mv 〈 0.196eV （95%） and Neff = 2.984 ± 0.826 （68%） are obtained, and when fixing Neff as the standard baseline 3.046, we attain ∑ mv 〈 0.240 eV （95%）. These constrained results are much tighter than the ones obtained by the current OHD, which makes the prospect of OHD in constraining cosmological parameters more promising as its accuracy and quantity grow.

Cosmological constraints on the Undulant Universe

We use the redshift Hubble parameter H（z） data derived from relative galaxy ages, distant type Ia supernovae （SNe Ia）, the Baryonic Acoustic Oscillation （BAO） peak, and the Cosmic Microwave Background （CMB） shift parameter data, to constrain cosmological parameters in the Undulant Universe. We marginalize the like- lihood functions over h by integrating the probability density 19 ∝ e-x^2/2. By using a Markov Chain Monte Carlo （MCMC） technique, we obtain the best fitting results and give the confidence regions in the b - Ωm0 plane. Then we compare their constraints. Our results show that the H（z） data play a similar role with the SNe Ia data in cosmological study. By presenting the independent and joint constraints, we find that the BAO and CMB data play very important roles in breaking the degeneracy compared with the H（z） and SNe Ia data alone. Combined with the BAO or CMB data, one can remarkably improve the constraints. The SNe Ia data sets constrain Ωm0 much tighter than the H（z） data sets, but the H（z） data sets constrain b much tighter than the SNe Ia data sets. All these results show that the Undulant Universe approaches the ACDM model. We expect more H（z） data to constrain cosmological parameters in the future.