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A dark energy is treated as a minimally coupled scalar fields. Both the cases of classical or tachyonic scalar fields have been considered. The evolution of scalar linear perturbations is studied, for a multi-component cosmological model, with the fluid approach used for description of components. For these scalar fields, the parameter “equation of state” is assumed to vary with time, w(a), and the other parameter, adiabatic sound speed, ca2, is assumed to be constant. The equations have been presented for background dynamics and evolution of scalar field density and velocity perturbations for synchronous gauge. These equations are inserted into CAMB code in order to test such model of dark energy with observational data. The 5-year WMAP data on CMB anisotropies were used, along with Union dataset on Supernovae Ia, the best-fit values of dark energy parameters were determined jointly with other main cosmological parameters. [ABSTRACT FROM AUTHOR]

The observational data on the large scale structure (LSS) of the Universe are used to establish the upper limit on the neutrino content marginalized over all other cosmological parameters within the class of adiabatic inflationary models. It is shown that the upper 2σ limit on the neutrino content can be expressed in the form Ω[sub v]h²/N[sup 0.64][sub v] ≤ 0.042 or, via the neutrino mass, m[sub v] ≤ 4.0eV. [ABSTRACT FROM AUTHOR]