We reconstruct evolution of the dark energy (DE) density using a nonparametric Bayesian approach from a combination of latest observational data. We caution against parameterizing DE in terms of its equation of state as it can be singular in modified gravity models, and using it introduces a bias preventing negative effective DE densities. We find a 3.7σ preference for an evolving effective DE density with interesting features. For example, it oscillates around the ΛCDM prediction at z ≤ 0.7, and could be negative at z ≥ 2.3; dark energy can be pressure-less at multiple redshifts, and a short period of cosmic deceleration is allowed at 0.1 ≤ z ≤ 0.2. We perform the reconstruction for several choices of the prior, as well as a evidence-weighted reconstruction. We find that some of the dynamical features, such as the oscillatory behaviour of the DE density, are supported by the Bayesian evidence, which is a first detection of a dynamical DE with a positive Bayesian evidence. The evidence-weighted reconstruction prefers a dynamical DE at a (2.5 ± 0.06)σ significance level.
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Wang, Y. (Creator), Pogosian, L. (Creator), Zhao, G. (Creator) & Zucca, A. (Creator), IOP Publishing, 20 Nov 2018