Matter power spectra in dynamical-Dark Energy cosmologies
  (abridged) We used a suite of numerical cosmological simulations in order to
investigate the effect of gas cooling and star formation on the large scale
matter distribution. The simulations follow the formation of cosmic structures
in five different Dark Energy models: the fiducial $\Lambda$CDM cosmology and
four models where the Dark Energy density is allowed to have a non-trivial
redshift evolution. For each cosmology we have a control run with dark matter
only, in order to allow a direct assessment of the impact of baryonic
processes. We found that the power spectra of gas and stars, as well as the
total matter power spectrum, are in qualitative agreement with the results of
previous works in the framework of the fiducial model, although several
quantitative differences exist. We used the halo model in order to investigate
the backreaction of gas and stars on the dark matter distribution, finding that
it is very well reproduced by increasing the average dark matter halo
concentration by 17%, irrespective of the mass. Moving to model universes
dominated by dynamical Dark Energy, it turns out that they introduce a specific
signature on the power spectra of the various matter components, that is
qualitatively independent of the exact cosmology considered. This generic shape
is well captured by the halo model, however the finer details of the dark
matter power spectrum can be precisely captured only at the cost of a few
slight modifications to the ingredients entering the model. The backreaction of
baryons onto the dark matter distribution works pretty much in the same way as
in the reference $\Lambda$CDM model. Nonetheless, the increment in average
concentration is less pronounced than in the fiducial model (only $\sim 10%$),
in agreement with a series of other clues pointing toward the fact that star
formation is less efficient when Dark Energy displays a dynamical evolution.
