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

TL;DR

Combining independent H(z) measurements with CMB data significantly tightens constraints on cosmological parameters, providing a robust test for deviations from the standard LCDM model and checking for systematic errors.

Contribution

This paper demonstrates that integrating H(z) data with CMB observations yields improved constraints on cosmological parameters, enhancing the robustness of LCDM model tests.

Findings

Neutrino mass sum constrained to < 0.5 eV at 68% confidence

Number of relativistic neutrino species N_rel estimated as 4.1^{+0.4}_{-0.9}

Dark energy equation of state w found to be -0.95 ± 0.17

Abstract

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 LCDM model. We show that independent determinations of the Hubble parameter H(z) such as those recently provided by Simon et al., Phys. Rev. D 71 (2005) 123001, combined with Cosmic Microwave Background data, can provide stringent constraints on possible deviations from the LCDM model. In particular we find that this data combination constrains at the 68% (95%) confidence level the following parameters: sum of the neutrino masses < 0.5 (1.0) eV, number of relativistic neutrino species N_rel = 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 \Omega_k = 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.