Parameter splitting in dark energy: is dark energy the same in the background and in the cosmic structures?

With the advent of precision cosmology, the constraints on new physics beyond the standard cosmological model are stronger than ever. However, some slight tensions have appeared between the cosmological parameters inferred by probes of the expansion of the Universe (mainly CMB and BAO) and the observations of the growth of cosmic structures. Moreover, the true origin of the cosmic acceleration is still unknown and alternative dynamical models or modifications of General Relativity have been proposed. I present an empirical consistency test of General Relativity/dark energy by disentangling expansion history and growth of structure constraints. In General Relativity within minimally coupled dark energy models, the expansion history fully determines the growth history, which is not necessarily true in modified gravity. In the context of standard wCDM, I 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 structures. If the null hypothesis is fulfilled (i.e. the two meta-parameters coincide) the underlying model is correct. If it is not, then it could be a hint of a failure in the model, the necessity of extensions to it or systematics in the data. Thus, combining different cosmological data sets, this consistency test also works as a probe for systematics and inconsistencies in the data. I present a global analysis using state-of-the-art cosmological data sets. We find that probes which depend on the growth of structures prefer a weaker growth than that inferred by background probes. I discuss the different possible scenarios which may lead to this result. The fact that the result is mostly driven by a sub-set of galaxy cluster abundance data points to the need of a better understanding of this probe before interpreting the result found as a failure of GR+wCDM.

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