Probing the interaction between dark energy and dark matter with the parametrized post-Friedmann approach

Abstract

There possibly exists some direct, non-gravitational coupling between dark energy and dark matter. This possibility should be seriously tested by using observations, which requires us to understand such a scenario from the aspects of both expansion history and growth of structure. It is found that once calculating the perturbations in the interacting dark energy (IDE) scenario, for most cases the curvature perturbation on superhorizon scales is divergent, which is a catastrophe for the IDE cosmology. We found a solution to this issue, which is to establish an effective theory to treat the dark energy perturbations totally based on the basic facts of dark energy. This scheme generalizes the parametrized post-Friedmann framework of uncoupled dark energy and can be used to cure the instability of the IDE cosmology. The whole parameter space of IDE models can henceforward be explored by observational data. The IDE scenario can thus be tested or falsified with current and future observational data by using the PPF approach. We expect that the future highly accurate observational data would offer the certain answer to the question whether there is a direct coupling between dark energy and dark matter.

Figures (2)

• Figure 1: The density perturbation evolutions at $k=0.1~\rm{Mpc}^{-1}$ in the IDE model with $Q^\mu=3\beta H\rho_c u_c^\mu$ in the synchronous gauge. The upper panels are obtained by using the previous method, and the lower panels are obtained within the PPF framework.
• Figure 2: The one- and two-dimensional posterior distributions for the parameters in the IDE model with $Q^\mu=3\beta H\rho_c u_c^\mu$.