Constraint on Coupled Dark Energy Models from Observations

TL;DR

This work tests whether a dynamical dark energy component, modeled as a quintessence field $\phi$ with an exponential potential $V(\phi)$, can be non-minimally coupled to cold dark matter through $\rho_{\rm c}(\phi)=\rho_{\rm c}^{*}e^{\beta\phi}$. By deriving the background and linear perturbation equations with a coupling term $Q_{\rm c}=\beta\dot{\phi}\rho_{\rm c}$ and implementing them in CAMB/CosmoMC, the authors perform a global fit to current cosmological data (CMB, BAO, SNIa, and ISW cross-correlations) and forecast how Planck-like and future surveys could improve constraints. They find that current observations constrain the coupling strength to $\beta<0.085$ (95% CL) with $\lambda<1.05$ (95% CL), while the ISW cross-correlation provides additional leverage when combined with background probes. Forecasts indicate future data could tighten these bounds by about a factor of two, underscoring the ISW signal and large-scale structure as powerful probes of dark-sector interactions. The results demonstrate that non-gravitational interactions between dark energy and dark matter leave measurable imprints on both CMB anisotropies and structure growth, with practical implications for testing alternatives to $\Lambda$CDM.$

Abstract

The coupled dark energy models, in which the quintessence scalar field nontrivially couples to the cold dark matter, have been proposed to explain the coincidence problem. In this paper we study the perturbations of coupled dark energy models and the effects of this interaction on the current observations. Here, we pay particular attention to its imprint on the late-time Integrated Sachs-Wolfe (ISW) effect. We perform a global analysis of the constraints on this interaction from the current observational data. Considering the typical exponential form as the interaction form, we obtain that the strength of interaction between dark sectors is constrained as $β<0.085$ at 95% confidence level. Furthermore, we find that future measurements with smaller error bars could improve the constraint on the strength of coupling by a factor two, when compared to the present constraints.

Figures (6)

• Figure 1: The cosmological evolutions of the cold dark matter and quintessence energy density parameters, $\Omega_{\,\rm i}$, for two models: $\lambda=1.22$, $\beta=0$ (black solid lines) and $\lambda=1.22$, $\beta=0.15$ (red dashed lines).
• Figure 2: The CMB temperature anisotropies and LSS matter power spectrum for two models: $\lambda=1.22$, $\beta=0$ (black solid lines) and $\lambda=1.22$, $\beta=0.15$ (red dashed lines).
• Figure 3: The cross-correlation signal $C_{\ell}^{gT}$ for two models: $\lambda=1.22$, $\beta=0$ (black solid lines) and $\lambda=1.22$, $\beta=0.15$ (red dashed lines).
• Figure 4: One dimensional posterior distributions of the strength of interaction $\beta$ from various data combinations: WMAP5 alone (black solid line), WMAP5+CMBExt (red dashed line), WMAP5+ISW (blue dash-dot line), all current data sets (magenta short dashed line), and all future data sets (navy blue short dash-dot line).
• Figure 5: Two dimensional marginalized contour in the ($\beta$, $\sigma_8$) panel from all current data sets (black solid lines) and all future data sets (red dash-dot lines), respectively.