CMB-Galaxy correlation in Unified Dark Matter Scalar Field Cosmologies
  We present an analysis of the cross-correlation between the CMB and the
large-scale structure (LSS) of the Universe in Unified Dark Matter (UDM) scalar
field cosmologies. We work out the predicted cross-correlation function in UDM
models, which depends on the speed of sound of the unified component, and
compare it with observations from six galaxy catalogues (NVSS, HEAO, 2MASS, and
SDSS main galaxies, luminous red galaxies, and quasars). We sample the value of
the speed of sound and perform a likelihood analysis, finding that the UDM
model is as likely as the LambdaCDM, and is compatible with observations for a
range of values of c_\infinity (the value of the sound speed at late times) on
which structure formation depends. In particular, we obtain an upper bound of
c_\infinity^2 \leq 0.009 at 95% confidence level, meaning that the LambdaCDM
model, for which c_\infinity^2 = 0, is a good fit to the data, while the
posterior probability distribution peaks at the value c_\infinity^2=10^(-4) .
Finally, we study the time dependence of the deviation from LambdaCDM via a
tomographic analysis using a mock redshift distribution and we find that the
largest deviation is for low-redshift sources, suggesting that future low-z
surveys will be best suited to constrain UDM models.
