Median Statistics and the Mass Density of the Universe

Abstract

We use weighted mean and median statistics techniques to combine individual estimates of Omega_m0, the present mean mass density in non-relativistic matter, and determine the observed values and ranges of Omega_m0 from different combinations of data. The derived weighted mean Omega_m0 values are not good representatives of the individual measurements, under the assumptions of Gaussianity and negligible correlation between the individual measurements. This could mean that some observational error bars are under-estimated. Discarding the most discrepant about 5% of the measurements generally alleviates but does not completely resolve this problem. While the results derived from the different combinations of data are not identical, they are mostly consistent, and a reasonable summary of the median statistics analyses is 0.2 <= Omega_m0 <= 0.35 at two standard deviations.Comment: 17 pages, submitted to Ap

Self-Interacting Holographic Dark Energy

“…In the first approach, the parameters of the model are θ = (H 0 , z acc , ω s ) therefore the 68.3% (1σ) or 95.4% We remark that our estimations of the actual Hubble parameter agree with the median statistics made in [104], namely, our value meets within the 1σ interval obtained with the median statistics, H 0 = 68 ± 5 kms −1 Mpc −1 , or with the analysis performed in [105] about the impact of H 0 prior on the evidence for dark radiation. On the other hand, we obtain C.L.…”

Constraints on Dark Energy From Baryon Acoustic Peak and Galaxy Cluster Gas Mass Measurements

“…Assuming the cold dark matter (CDM) model of structure formation (for a discussion of apparent problems with this model, see Peebles & Ratra 2003, and references therein), and assuming that the dark energy is a time-independent cosmological constant (see, e.g., Wang & Mukherjee 2007;Gong et al 2008;Ichikawa & Takahashi 2008;Virey et al 2008), CMB anisotropy data combined with independent dark matter density measurements (see, e.g., Chen & Ratra 2003b) are consistent with negligible spatial curvature (see, e.g., Podariu et al 2001b;Page et al 2003;Spergel et al 2007;Doran et al 2007). CMB anisotropy data in combination with the low measured density of nonrelativistic matter then require the presence of dark energy and so are consistent with the SNIa results.…”

The Hubble parameter in the early universe with viscous QCD matter and finite cosmological constant

“…Also, the cosmological constant seems to be essential. The motivation of finite Λ is based on theoretical needs and astrophysical and cosmological observations [25][26][27][28][29][30]37]. It is very essential to describe the early stages of universe, Eq.…”

“…Furthermore, it seems that the flat universe contains both matter and cosmological constant Λ so that Λ = 0.06 +0.28 −0.34 or for a stringent upper limit < 0.51 (at the 95% confidence level). On the other hand, there are many observations indicating that the non-relativistic matter contributes with ∼ 1/3 of the critical density [28]. In other words, such observations would also mean that the universe contains ∼ 2/3 of its total energy density in form of dark energy.…”