Dark Matter and Dark Energy Interactions: Theoretical Challenges, Cosmological Implications and Observational Signatures

TL;DR

This work surveys theoretical frameworks and observational tests of interactions between dark matter and dark energy, arguing such couplings can alleviate the coincidence problem and connect to modified gravity. It compares phenomenological fluid models and field-based descriptions, including holographic dark energy, and analyzes both background dynamics and linear/nonlinear perturbations, as well as nonperturbative aspects like Layzer–Irvine and spherical collapse. The paper synthesizes constraints from CMB, SN, BAO, RSD, ISW, and cluster counts, highlighting that current data allow small couplings with a tendency toward energy transfer from dark energy to dark matter. It also outlines current and future observational avenues (Stage III/IV surveys and CMB missions) that will sharpen tests of the dark-sector interaction and potentially reveal new physics beyond ΛCDM.

Abstract

Models where Dark Matter and Dark Energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

Figures (21)

• Figure 1: Evolution of energy densities on a interacting DM/DE model with kernel $Q=H\xi(\rho_{d}+\rho_{c})$. Lines correspond to: Baryons (solid), DM (dashed), DE (dot-dashed) with an EoS parameter $\omega_d=-1.1$ and radiation (triple dot-dashed). In (a) $\xi=0.1$ and in (b) $\xi=0.01$.
• Figure 2: Evolution of the ratio of DM to DE densities for different model parameters. In (a) the kernel is $Q=H\xi (\rho_{c}+\rho_{d})$ and in (b) $Q=H\xi_1\rho_{c}$. The solid line, common to both panels, corresponds to the concordance model, while the dashed lines correspond to different interaction kernel parameters.
• Figure 3: Selected curves $\chi(s)$ for a DE EoS parameter $\omega_d =-1.1$ and $r_{0} =3/7$ and three different values of $\xi$. The thick lines correspond to the past evolution in the interval $z=[0,20]$ and the thin lines to the future evolution in $z=[-0.9,0]$.
• Figure 4: Density parameter $\Omega$ (left panel) and equation of state parameter $w$ and deceleration parameter (right panel) for the model given by eqs. (\ref{['varphi_6']}-\ref{['rho_6_dm']}). The interaction term has been explicitly separated.
• Figure 5: Variation of the CMB radiation power spectrum with cosmological parameters.