Dark sectors of the Universe: A Euclid survey approach
  In this paper we study the consequences of relaxing the hypothesis of the
pressureless nature of the dark matter component when determining constraints
on dark energy. To this aim we consider simple generalized dark matter models
with constant equation of state parameter. We find that present-day
low-redshift probes (type-Ia supernovae and baryonic acoustic oscillations)
lead to a complete degeneracy between the dark energy and the dark matter
sectors. However, adding the cosmic microwave background (CMB) high-redshift
probe restores constraints similar to those on the standard $\Lambda$CDM model.
We then examine the anticipated constraints from the galaxy clustering probe of
the future Euclid survey on the same class of models, using a Fisher forecast
estimation. We show that the Euclid survey allows us to break the degeneracy
between the dark sectors, although the constraints on dark energy are much
weaker than with standard dark matter. The use of CMB in combination allows us
to restore the high precision on the dark energy sector constraints.
