Current Status of Models with Hot and Cold Dark Matter

Details Current Status of Models with Hot and Cold Dark Matter Current Status of Models with Hot and Cold Dark Matter

Mar 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001arep...45..163m&link_type=abstract

Astronomy Reports, Volume 45, Issue 3, March 2001, pp.163-172

Astronomy and Astrophysics

Astronomy

2

Scientific paper

An analysis of a five-parameter family of cosmological models in a spatially flat Friedmann Universe with a zero Λ term is presented. The five parameters are (1) σ8, the dispersion of the mass fluctuations in a sphere with radius 8h -1 Mpc, where h=H 0/100 km s-1 Mpc-1 and H 0 is the Hubble constant; (2) n, the slope of the density-perturbation spectrum; (3) Ωv, the normalized energy density of hot dark matter; (4) Ωb, the baryon density; and (5) h, the normalized Hubble constant. The density of cold dark matter is determined from the condition Ω cdm >1-Ωv-Ω b . Analysis of the models is based on comparison of computational results with observational data for: (1) the number density and mass function of galaxy clusters (a so-called Press-Schechter formalism) and (2) the cosmic microwave background anisotropy. The first method enabled us to determine the value σ8=0.52±0.01 with high accuracy. Using the resulting normalization of the density-perturbation spectrum, we calculated a model for the anisotropy of the cosmic microwave background radiation on large scales (l⋍10, where l is the harmonic number) and the required contribution of cosmological gravitational waves, characterized by the parameter T/S. The restrictions on T/S become weaker as Ωv increases. Nevertheless, even when Ωv≤0.4, models with h+n≥1.5 require a considerable contribution from gravitational waves: T/S≳0.3. On the other hand, in models with Ωv≤0.4 and a scale-invariant density-perturbation spectrum (n=1), we find T/S ≳10(h-0.47). The minimization of T/S is possible only for the family of models with red spectra (n<1) and small h (<0.6). The value of Ωv is determined most accurately by the data onΔT/T near the first acoustic peak (l⋍200). By imposing a general restriction on the amplitude of gravitational waves T/S∈[0, 3] and taking into account the available observational data on the amplitude of the acoustic peak of Sakharov oscillations, ranges of possible values n and Ωv are derived. If the baryon number is constrained by nucleosynthesis data, the models under consideration can have both moderately red and blue power spectra n∈[0.9, 1.2] with a rather high concentration of hot particles Ωv∈[0.2,0.4]. The conditions that n<0.9 and/or Ωv<0.2 decrease the relative amplitude of the acoustic peak by over 30% compared to its value in the standard cold-dark-matter (CDM) model normalized using COBE data.

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