Cosmological constraints on coupled dark energy

TL;DR

This study assesses cosmological constraints on phenomenological coupled dark energy models with a coupling form $\bar{Q}=3H\xi_x\bar{\rho}_x$, examining both background evolution and linear perturbations. By introducing rest-frame and perturbed-H choices via parameters $b_1$ and $b_2$, four IDE variants (IDE1–IDE4) are analyzed through derived perturbation equations, ensuring stability with $c^2_{sA}=1$. Employing Planck 2015 CMB, BAO, SNIa, RSD, and weak-lensing data, the authors constrain the interaction rate $\xi_x$, finding no evidence for interaction at $2\sigma$ and similar bounds across all IDE models, with $\xi_x$ best-fit at a few $\times 10^{-3}$ and cosmological parameters such as $\Omega_m$, $H_0$, and $\sigma_8$ remaining consistent. The results imply current data cannot decisively distinguish the four coupled models, and highlight the importance of nonlinear-scale modeling for future refinements.

Abstract

The coupled dark energy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as $\bar{Q}=3Hξ_x\barρ_x$, which is related to the interaction rate and energy density of dark energy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, $fσ_8(z)$ data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us there is no evidence of interaction at 2$σ$ level, it is very hard to distinguish different coupled models from other ones.

Figures (2)

• Figure 1: The 1D marginalized distributions on the parameters $\xi_x$, $w_x$, $\Omega_m$ and 2D contours of the four coupled models with 68% C.L., 95 % C.L., and 99.7% C.L. between each other, where CMB from Planck 2015, BAO, SNIa, RSD, and WL data sets have been used. The color map of IDE1, IDE2, IDE3, IDE4 are, respectively, black, red, green, blue.
• Figure 2: In contrast to the 1D marginalized distributions on the parameters $\xi_x$, $w_x$, $\Omega_m$, $\sigma_8$ of the four coupled models with 68% C.L., 95 % C.L., and 99.7% C.L. between each other, where CMB from Planck 2015, BAO, SNIa, RSD, and WL data sets have been used. The line style of IDE1, IDE2, IDE3, IDE4 are, respectively, black solid, red dashed, green dotted-dashed, blue dotted.