Observational constraints on scalar field models of dark energy with
  barotropic equation of state
  We constrain the parameters of dynamical dark energy in the form of a
classical or tachyonic scalar field with barotropic equation of state jointly
with other cosmological ones using the combined datasets which include the CMB
power spectra from WMAP7, the baryon acoustic oscillations in the space
distribution of galaxies from SDSS DR7, the power spectrum of luminous red
galaxies from SDSS DR7 and the light curves of SN Ia from 2 different
compilations: Union2 (SALT2 light curve fitting) and SDSS (SALT2 and MLCS2k2
light curve fittings). It has been found that the initial value of dark energy
equation of state parameter is constrained very weakly by most of the data
while the rest of main cosmological parameters are well constrained: their
likelihoods and posteriors are similar, have the forms close to Gaussian (or
half-Gaussian) and their confidential ranges are narrow. The most reliable
determinations of the best fitting value and $1\sigma$ confidence range for the
initial value of dark energy equation of state parameter were obtained from the
combined datasets including SN Ia data from the full SDSS compilation with
MLCS2k2 fitting of light curves. In all such cases the best fitting value of
this parameter is lower than the value of corresponding parameter for current
epoch. Such dark energy loses its repulsive properties and in future the
expansion of the Universe will change into contraction. We also perform an
error forecast for the Planck mock data and show that they narrow essentially
the confidential ranges of cosmological parameters values, moreover, their
combination with SN SDSS compilation with MLCS2k2 light curve fitting may
exclude the fields with initial equation of state parameter $>-0.1$ at
2$\sigma$ confidential level.
