New constraints on Coupled Dark Energy from Planck

TL;DR

The paper tests whether a coupling between dark matter and dark energy can reconcile Planck CMB measurements with local $H_0$ determinations by using a model with $Q = \xi \mathcal{H} \rho_{de}$ in a flat FRW universe. It adapts CAMB/CosmoMC to fit Planck data (with optional HST and BAO priors) across a seven-parameter space including the coupling $\xi$ and examines how the coupling alters the CMB spectrum, degeneracies, and inferred $H_0$. The main findings are that Planck data allow a weakly negative coupling ($\xi \approx -0.49$ at 68% c.l.), and Planck+HST data prefer a nonzero negative coupling at 95% c.l., which can raise $H_0$ and alleviate the tension. The results indicate a possible dark-sector interaction that impacts cosmological inferences and encourages future observations to break degeneracies and confirm or refute such coupling.

Abstract

We present new constraints on coupled dark energy from the recent measurements of the Cosmic Microwave Background Anisotropies from the Planck satellite mission. We found that a coupled dark energy model is fully compatible with the Planck measurements, deriving a weak bound on the dark matter-dark energy coupling parameter ξ=-0.49^{+0.19}_{-0.31} at 68% c.l.. Moreover if Planck data are fitted to a coupled dark energy scenario, the constraint on the Hubble constant is relaxed to H_0=72.1^{+3.2}_{-2.3} km/s/Mpc, solving the tension with the Hubble Space Telescope value. We show that a combined Planck+HST analysis provides significant evidence for coupled dark energy finding a non-zero value for the coupling parameter ξ, with -0.90< ξ<-0.22 at 95% c.l.. We also consider the combined constraints from the Planck data plus the BAO measurements of the 6dF Galaxy Survey, the Sloan Digital Sky Survey and the Baron Oscillation Spectroscopic Survey.

Figures (10)

• Figure 1: CMB temperature power spectrum in the $\Lambda$CDM case and in the coupled cases for $\xi=-0.2, -0.5$, $\Omega_c h^2= 0.1186$, $H_0=67.9$ km/s/Mpc. The main effects of the coupling are shifting the position of the acoustic peaks and varying their amplitude.
• Figure 2: Posterior distributions for the cosmological parameters presented in Tab.\ref{['Tab1']} from PLANCK data set alone (solid black line), PLANCK plus HST prior (red dashed line) and PLANCK plus BAO measurements (blue dot-dashed line). The effect of HST prior is to provide narrower distributions and stronger constraints, especially for the coupling parameter $\xi$.
• Figure 3: 2-D posterior distributions of parameters most degenerate with the coupling $\xi$. A strong correlation is evident with the cold dark matter density parameter. A larger absolute value of the coupling $\xi$ implies a decrement of the dark cold matter and a consequent decrease of the dark matter density. Since the assumption of a flat universe, it also implies a larger dark energy amount that brings to an increment of $H_0$ and consequently an increase of $\theta$.
• Figure 4: 2-D posterior distributions in presence of the HST prior for the same parameters shown in Fig.\ref{['fig.2Dcontour']}.
• Figure 5: 2-D posterior distributions in presence of the HST prior for the same parameters shown in Fig.\ref{['fig.2Dcontour']}.