The Case for Omega_M = 0.33 +/- 0.035

TL;DR

The paper addresses the problem of determining the mean matter density $\Omega_M$ without bias from light distribution. It uses a physically based approach combining CMB anisotropy, matter power spectrum, BBN baryon density, cluster baryon fractions, and the Hubble constant to jointly constrain $\Omega_M$, $\Omega_B$, and $h$ via a likelihood analysis. The main result is $\Omega_M = 0.33 \pm 0.035$, $\Omega_B = 0.039 \pm 0.0075$, and $h = 0.69 \pm 0.06$, with a derived dark-energy density $\Omega_X = 0.67 \pm 0.06$ under flatness. The findings support a Universe with dark energy and show a higher matter density than cluster mass-to-light estimates, indicating light-production biases; the work also outlines future improvements with MAP/Planck and large redshift surveys that will sharpen constraints and help break degeneracies in the dark-energy equation of state $w_X$.

Abstract

For decades, the determination of the mean density of matter(Omega_M) has been tied to the distribution of light. This has led to a ``bias,'' perhaps as large as a factor of 2, in determining a key cosmological parameter. Recent measurements of the physical properties of clusters, cosmic microwave background (CMB) anisotropy and the power spectrum of mass inhomogeneity now allow a determination of Omega_M without ``visual bias.'' The early data lead to a consistent picture of the matter and baryon densities, with Omega_B = 0.039 +/- 0.0075 and Omega_M = 0.33 +/- 0.035.