Constraining dark energy dynamics in extended parameter space

Dynamical dark energy has been recently suggested as a promising and physical way to solve the 3 sigma tension on the value of the Hubble constant H0 between the direct measurement of Riess et al. (2016) (R16, hereafter) and the indirect constraint from cosmic microwave anisotropies obtained by the Planck satellite under the assumption of a ΛCDM model. In this paper, by parametrizing dark energy evolution using the w0-wa approach, and considering a 12 parameter extended scenario, we find that: (a) the tension on the Hubble constant can indeed be solved with dynamical dark energy, (b) a cosmological constant is ruled out at more than 95% c.l. by the Planck+R16 dataset, and (c) all of the standard quintessence and half of the "downward going" dark energy model space (characterized by an equation of state that decreases with time) is also excluded at more than 95% c.l. These results are further confirmed when cosmic shear, CMB lensing, or SN Ia luminosity distance data are also included. The best fit value of the χ2 for the Planck+R16 data set improves by Δχ2=-12.9 when moving to 12 parameters respect to standard ΛCDM. However, tension remains with the BAO dataset. A cosmological constant and small portion of the freezing quintessence models are still in agreement with the Planck+R16+BAO data set at between 68% and 95% c.l. Conversely, for Planck plus a phenomenological H0 prior, both thawing and freezing quintessence models prefer a Hubble constant of less than 70 km/s/Mpc. The general conclusions hold also when considering models with nonzero spatial curvature.