The dynamics of expansion and large scale structure formation of the Universe are analyzed for models with dark energy in the form of a phantom scalar field which initially mimics a Λ-term and evolves slowly to the Big Rip singularity. The discussed model of dark energy has three parametersthe density and the equation of state parameter at the current epoch, Ω de and w0, and the asymptotic value of the equation of state parameter at a → ∞, c 2 a . Their best-fit values are determined jointly with all other cosmological parameters by the MCMC method using observational data on CMB anisotropies and polarization, SNe Ia luminosity distances, BAO measurements and more. Similar computations are carried out for ΛCDM and a quintessence scalar field model of dark energy. It is shown that the current data slightly prefer the phantom model, but the differences in the maximum likelihoods are not statistically significant. It is also shown that the phantom dark energy with monotonically increasing density in future will cause the decay of large scale linear matter density perturbations due to the gravitational domination of dark energy perturbations long before the Big Rip singularity.PACS numbers: 95.36.+x, 98.80.-k

The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state (EoS) are analyzed. It is shown that the past dynamics of expansion and future of the Universe -eternal accelerated expansion or turnaround and collapse -are completely defined by the current energy density of a scalar field and relation between its current and early EoS parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the "effective sound speed" of a scalar field, defined by its Lagrangian. It is concluded that such scalar fields with different values of these parameters are distinguishable in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year WMAP data on CMB anisotropies, the Union2 dataset on Supernovae Ia and SDSS DR7 data on luminous red galaxies (LRG) space distribution. Using the Markov Chain Monte Carlo technique the marginalized posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper. PACS numbers: 95.36.+x, 98.80.-k Keywords: cosmology: dark energy-scalar field-cosmic microwave background-large scale structure of Universe-cosmological parameters

The locations and amplitudes of three acoustic peaks and two dips in the BOOMERANG, MAXIMA, and DASI measurements of the cosmic microwave background (CMB) anisotropy power spectra as well as their statistical confidence levels are determined in a model-independent way. It is shown that the BOOMERANG 2001 data from Netterfield and coworkers fix the location and amplitude of the first acoustic peak at more than 3 confidence. The next two peaks and dips are determined at a confidence level above 1 but below 2 . The locations and amplitudes of the first three peaks and two dips are l p 1 ¼ 212 AE 17,(1 errors include statistical and systematic errors). The MAXIMA and DASI experiments give similar values for the extrema that they determine. For MAXIMA these are the first and third peaks, for DASI the first and second peaks and the first dip. Moreover, the locations and amplitudes of the extrema determined from the combined data of all experiments are quite close to the corresponding values extracted from the BOOMERANG data alone. In order to use these data in a fast search for cosmological parameters, an accurate analytic approximation to calculate CMB peak and dip positions and amplitudes in mixed dark matter models with cosmological constant and curvature is derived and tested. The determined cosmological parameters from the CMB acoustic extrema data show good agreement with other determinations, especially with the baryon content as deduced from standard nucleosynthesis constraints, as shown by Burles and coworkers. These data supplemented by constraints from direct measurements of some cosmological parameters and data on large-scale structure lead to a best-fit model that agrees with practically all the used experimental data within 1 . The best-fit parameters are à ¼ 0

The development of perturbations of number densities of ions and electrons during the recombination epoch is analysed. The equations for relative perturbations of ionization fractions were derived from the system of equations for accurate computation of the ionization history of the early Universe. It is shown that strong dependence of ionization and recombination rates on the density and temperature of plasma provides the significant deviations of amplitudes of ionization fractions relative to perturbations from those of baryon matter density adiabatic perturbations. Such deviations are most prominent for cosmological adiabatic perturbations of scales larger than the sound horizon at the recombination epoch. The amplitudes of relative perturbations of number densities of electrons and protons at the last scattering surface exceed by a factor of ≃5 the amplitude of the relative perturbation of baryons total number density: for helium ions this ratio reaches a value of ≃18. For subhorizon cosmological perturbations, these ratios appear to be essentially smaller and depend on oscillation phase at the moment of decoupling. These perturbations of number densities of ions and electrons at the recombination epoch do not contribute to the intrinsic plasma temperature fluctuations but cause the ‘corrugation’ of the last scattering surface in optical depth, δzdec/(zdec+ 1) ≈−δb/3, at scales larger than the sound horizon. It may result in notable changes of pre‐calculated values of the cosmic microwave background polarization pattern at several degrees of angular scales.

We determine the best-fit values and confidence limits for dynamical dark energy parameters together with other cosmological parameters on the basis of different datasets which include WMAP9 or Planck-2013 results on CMB anisotropy, BAO distance ratios from recent galaxy surveys, magnitude-redshift relations for distant SNe Ia from SNLS3 and Union2.1 samples and the HST determination of the Hubble constant. We use a Markov Chain Monte Carlo routine to map out the likelihood in the multi-dimensional parameter space. We show that the most precise determination of cosmological parameters with the narrowest confidence limits is obtained for the Planck+HST+BAO+SNLS3 dataset. The best-fit values and 2σ confidence limits for cosmological parameters in this case are Ω de = 0.718 ± 0.022, w 0 = −1.15 +0.14 −0.16 , c 2 a = −1.15 +0.02 −0.46 , Ω b h 2 = 0.0220 ± 0.0005, Ω cdm h 2 = 0.121 ± 0.004, h = 0.713 ± 0.027, n s = 0.958 +0.014 −0.010 , A s = (2.215 +0.093 −0.101 ) cdot10 −9 , τ rei = 0.093 +0.022 −0.028 . For this dataset, the ΛCDM model is just outside the 2σ confidence region, while for the dataset WMAP9+HST+BAO+SNLS3 the ΛCDM model is only 1σ away from the best fit. The tension in the determination of some cosmological parameters on the basis of two CMB datasets WMAP9 and Planck-2013 is highlighted.