  The latest cosmological observables analyses seem to converge to a concordant
view of the cosmological model: namely the power law Lambda-CDM. The recent
WMAP results comfort this new standard model. Nevertheless, some degeneracy in
the CMB physics do not allow one to exclude alternative models. A combined
analysis with other cosmological observations is thus needed. An example of
such work is shown here, focusing on the abundance of local clusters. The
latter is a traditional way to derive the amplitude of matter fluctuations, but
which suffers from a lack of accurate knowledge of their masses. Here we show
that the mass temperature relation can be specified for any cosmological model
from consistency arguments, removing most of this uncertainty. This allows to
obtain an estimation of the amplitude of matter fluctuations with an accuracy
of 5%. Quite remarkably, this amplitude can be also tightly constrained from
existing CMB measurements. However, the amplitude inferred in this way in a
concordance model (Lambda-CDM) is significantly larger than the value derived
from x-ray clusters. Such a discrepancy may reveal the existence of a new dark
component in the Universe. It may alternatively reveal a significant depletion
of the gas during the formation of clusters. In all cases, an essential element
of clusters formation history seems to be missing.
