Can interacting dark energy solve the $H_0$ tension?

The answer is yes. We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant $H_0$ between the cosmic microwave background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two data sets points toward a nonzero dark matter-dark energy coupling $\xi$ at more than two standard deviations, with $\xi =-0.26_{-0.12}^{+0.16}$ at 95% C.L., i.e. with a moderate evidence for interacting dark energy with an odds ratio of $6:1$ respect to a non interacting cosmological constant. However the $H_0$ tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantomlike equation of state $w=-1.185\pm 0.064$ (at 68% C.L.), ruling out the pure cosmological constant case, $w=-1$, again at more than two standard deviations. When Planck data are combined with external datasets, as BAO, JLA Supernovae Ia luminosity distances, cosmic shear or lensing data, we find perfect consistency with the cosmological constant scenario and no compelling evidence for a dark matter-dark energy coupling.

Figure 1

68% and 95% C.L. in the two-dimensional ($\xi$, $H_0$) planes from the “$\mathrm{Planck}\mathrm{TT}+\mathrm{lowTEB}$” dataset (left panel) and “$\mathrm{Planck}\mathrm{TTTEEE}+\mathrm{lowTEB}$” dataset (right panel) also combined with the R16 prior on the Hubble constant. Notice that the presence of a coupling $\xi$ allows for larger values for $H_0$ from Planck data. The inclusion of the R16 prior results in an indication for $\xi <0$ with a significance above two standard deviations.

Figure 2

Left panel: 68% and 95% C.L. in the two-dimensional (${\mathrm{\Omega }}_m$, ${\sigma }_8$) plane from the “$\mathrm{Planck}\mathrm{TTTEEE}+\mathrm{lowTEB}$” dataset for a pure $\mathrm{\Lambda }\mathrm{CDM}$ scenario, a varying $\xi$ interacting model, and also adding to the former the WL data set. Notice that the coupling allows for larger values for ${\sigma }_8$ and smaller values for ${\mathrm{\Omega }}_m$, relaxing the Planck bounds on the $S_8$ parameter and mildly alleviating the tension with the $S_8$ values measured by cosmic shear surveys as CFHTLenS and KiDS-450. Right panel: 68% and 95% C.L. in the two-dimensional ($\xi$, $\tau$) plane from the “Planck TTTEEE ” data set, and also combined with the “tau055” prior on the reionization optical depth. Notice that the “tau055” prior affects only marginally the constraints on $\xi$, resulting in a $\sim 1\sigma$ indication for $\xi <0$ (after marginalization over $\tau$).

Figure 3

Left panel: 68% and 95% C.L. in the two-dimensional ($w$, $H_0$) plane from the combination of “$\mathrm{Planck}\mathrm{TTTEEE}+\mathrm{lowTEB}$” measurements (grey contours), “$\mathrm{Planck}\mathrm{TTTEEE}+\mathrm{lowTEB}+\mathrm{R}16$” (red contours) and “$\mathrm{Planck}\mathrm{TTTEEE}+\mathrm{lowTEB}+\mathrm{BAO}$” (blue contours), for an interacting dark matter-dark energy scenario. Right panel: As in the left panel but with $\xi =0$.