New Limits on Coupled Dark Energy from Planck

TL;DR

Addresses whether the current acceleration arises from dark energy or modified gravity. The study analyzes coupled dark energy with a quintessence field interacting with cold dark matter through a coupling $\beta$, using Planck data and supplementary BAO, SNIa, and CMB lensing to constrain $\beta$ and search for a non-zero coupling. The analysis solves the background and perturbation equations with $Q=\beta\dot{\phi}\rho_c$ and an exponential potential $V(\phi)=V_0 e^{-\lambda\phi}$ and performs CosmoMC parameter estimation. Findings include $\beta<0.102$ (95% C.L.) from Planck+WP alone and $\beta<0.052$ (95% C.L.) with normal low-redshift data; tension datasets including HST $H_0$ priors and SNLS suggest a non-zero coupling around $\beta\approx 0.07$–$0.08$ at 68% CL but are not conclusive. Significance: indicates potential dark-sector interaction under current data but emphasizes limitations due to H0 tensions and dataset systematics; further data are needed to confirm or refute a dark-sector interaction.

Abstract

Recently, the Planck collaboration has released the first cosmological papers providing the high resolution, full sky, maps of the cosmic microwave background (CMB) temperature anisotropies. It is crucial to understand that whether the accelerating expansion of our universe at present is driven by an unknown energy component (Dark Energy) or a modification to general relativity (Modified Gravity). In this paper we study the coupled dark energy models, in which the quintessence scalar field nontrivially couples to the cold dark matter, with the strength parameter of interaction $beta$. Using the Planck data alone, we obtain that the strength of interaction between dark sectors is constrained as $beta < 0.102$ at $95%$ confidence level, which is tighter than that from the WMAP9 data alone. Combining the Planck data with other probes, like the Baryon Acoustic Oscillation (BAO), Type-Ia supernovae ``Union2.1 compilation'' and the CMB lensing data from Planck measurement, we find the tight constraint on the strength of interaction $beta < 0.052$ ($95%$ C.L.). Interestingly, we also find a non-zero coupling $beta = 0.078 pm 0.022$ ($68%$ C.L.) when we use the Planck, the ``SNLS'' supernovae samples, and the prior on the Hubble constant from the Hubble Space Telescope (HST) together. This evidence for the coupled dark energy models mainly comes from a tension between constraints on the Hubble constant from the Planck measurement and the local direct $H_0$ probes from HST.

Figures (5)

• Figure 1: The CMB temperature anisotropies for two different models: $\lambda=1.22$, $\beta=0$ (black solid lines) and $\lambda=1.22$, $\beta=0.15$ (red dashed lines).
• Figure 2: Marginalized two-dimensional likelihood (1, $2\,\sigma$ contours) constraints on the parameters $\beta$ and $\sigma_8$ in the coupled dark energy model from the Planck+WP (red) and WMAP9 (blue) data, respectively.
• Figure 3: One-dimensional posterior distributions of the strength of interaction $\beta$ from various data combinations: Planck+WP+BAO (red dashed line), Planck+WP+Union (blue dotted line), Planck+WP+Lens (magenta dash-dotted line), all "Normal Data" together (black solid line).
• Figure 4: One-dimensional posterior distributions of the strength of interaction $\beta$ and the Hubble constant $H_0$ from various data combinations: Planck+WP (red dotted line), Planck+WP+HST (blue dashed line), Planck+WP+SNLS (magenta dash-dotted line), all "Tension Data" together (black solid line). The vertical blue dashed line in the right panel denotes the HST prior on the Hubble constant.
• Figure 5: Marginalized two-dimensional likelihood (1, $2\,\sigma$ contours) constraints on the parameters $\beta$ and $H_0$ in the coupled dark energy model from Planck+WP alone (green), "Normal" data (red) and "Tension" data (blue), respectively.