Constraints on interacting dark energy models from Planck 2015 and redshift-space distortion data

TL;DR

The paper assesses phenomenological interactions between dark matter and dark energy by confronting four coupling models, defined via $Q=3H(\lambda_1\rho_c + \lambda_2\rho_d)$, with Planck 2015 CMB data, BAO, SNIa, H0 priors, and redshift-space distortions. Using CAMB and CosmoMC, it analyzes both background evolution and linear perturbations in synchronous gauge, revealing that energy transfer from dark matter to dark energy is strongly disfavored, while energy flow from dark energy to dark matter is favored in some data combinations, potentially addressing the coincidence problem. Planck 2015 tightens constraints on Models III and IV, and when RSD data are included, Model I is ruled out, whereas Model II shows a preference for a small positive coupling around $\lambda_2\sim 0.02$ with $w$ near $-1$, though a zero coupling remains disfavored only in some joint analyses. The results demonstrate that complementary RSD measurements are powerful for breaking degeneracies and testing dark sector interactions, suggesting that coupled dark energy remains a viable framework for describing late-time cosmology, albeit with model-dependent conclusions and some residual tensions between CMB and low-redshift observations.

Abstract

We investigate phenomenological interactions between dark matter and dark energy and constrain these models by employing the most recent cosmological data including the cosmic microwave background radiation anisotropies from Planck 2015, Type Ia supernovae, baryon acoustic oscillations, the Hubble constant and redshift-space distortions. We find that the interaction in the dark sector parameterized as an energy transfer from dark matter to dark energy is strongly suppressed by the whole updated cosmological data. On the other hand, an interaction between dark sectors with the energy flow from dark energy to dark matter is proved in better agreement with the available cosmological observations. This coupling between dark sectors is needed to alleviate the coincidence problem.

Figures (8)

• Figure 1: The growth rate $f$ as a function of the wave number $k$. The blue line is for $f = \frac{d\ln{\delta_m}}{d\ln{a}}$, the orange line is for $f= \left(\frac{\sigma_{vd}}{\sigma_8}\right)^2$ and the green line is for $f= \Omega_m^{0.545}$.
• Figure 2: Evolutions of $f$ and $f\sigma_8(z)$ as a function of redshift. The blue line is for Model I, the orange line for Model II, the green line for Model III and the red line is for Model IV. All lines are plotted with the same strength of the interaction, $\lambda_i= 0.1$, where the equations of state of dark energy are taken as $\omega \approx -1$. The purple line is the best fit for Model II, as described in the sixth column of Table \ref{['tab.model2_RSD']}, and the brown line is plotted with the same parameters, but without the interaction. We include the data in Table \ref{['RSD']} with corresponding error bars in the right panel.
• Figure 3: 1-D distribution for selected parameters.
• Figure 4: 2-D distribution for selected parameters.
• Figure 5: 1-D distribution for selected parameters using RSD data.