Parameter splitting in dark energy: is dark energy the same in the
  background and in the cosmic structures?
  We perform an empirical consistency test of General Relativity/dark energy by
disentangling expansion history and growth of structure constraints. We replace
each late-universe parameter that describes the behavior of dark energy with
two meta-parameters: one describing geometrical information in cosmological
probes, and the other controlling the growth of structure. If the underlying
model (a standard wCDM cosmology with General Relativity) is correct, that is
under the null hypothesis, the two meta-parameters coincide. If they do not, it
could indicate a failure of the model or systematics in the data. We present a
global analysis using state-of-the-art cosmological data sets which points in
the direction that cosmic structures prefer a weaker growth than that inferred
by background probes. This result could signify inconsistencies of the model,
the necessity of extensions to it or the presence of systematic errors in the
data. We examine all these possibilities. The fact that the result is mostly
driven by a specific sub-set of galaxy clusters abundance data, points to the
need of a better understanding of this probe.
