Reconciling CMB and structure growth measurements with dark energy interactions

TL;DR

This work introduces a Type-3 pure momentum-transfer coupled quintessence model in which the dark sector exchanges momentum but not energy at the background level, preserving standard background densities while altering perturbations. Using a Planck TT, BAO, JLA, and SZ cluster data suite, the authors perform MCMC inference and find that negative coupling values $\beta$ can suppress growth, making the model as compatible as $\Lambda$CDM with CMB+BAO data and strongly preferred once cluster data are added. The results show that the model can reduce $\sigma_8$, modestly shift $\Omega_M$, and yield a competitive or improved fit (lower $\chi^2$) relative to $\Lambda$CDM, though a tension with local $H_0$ measurements persists. These findings suggest a promising avenue for resolving CMB-LSS tensions, motivating further non-linear simulations and model-agnostic parameterizations to robustly constrain Type-3-like momentum-transfer models.

Abstract

We study a coupled quintessence model with pure momentum exchange and present the effects of such an interaction on the Cosmic Microwave Background (CMB) and matter power spectrum. For a wide range of negative values of the coupling parameter $β$ structure growth is suppressed and the model can reconcile the tension between Cosmic Microwave Background observations and structure growth inferred from cluster counts. We find that this model is as good as $Λ$CDM for CMB and baryon acoustic oscillation (BAO) data, while the addition of cluster data makes the model strongly preferred, improving the best-fit $χ^2$-value by more than $16$.

Figures (7)

• Figure 1: Comparison of the CMB TT power spectra (left panel) and the linear (total) matter power spectra $P(k)$ at $z=0$ (right panel). Black solid lines denote the uncoupled quintessence model, blue dotted lines denote the coupled model with positive coupling parameter $\beta=0.1$, and dashed red lines denote the coupled model with negative coupling parameter $\beta=-0.5$.
• Figure 2: Comparison of the CMB TT power spectra (left panel) and the linear (total) matter power spectra at $z=0$ (right panel) for a wide range of negative $\beta$-values. In both cases we show the ratio between the $\text{T3}_\text{ph}$ model and the predictions of the uncoupled quintessence model.
• Figure 3: The evolution of the dark energy equation of state parameter $w_\phi = \bar{P}_\phi /\bar{\rho}_\phi$ as a function of the coupling parameter $\beta$. A constant $w_\phi = -0.9$ is shown for comparison.
• Figure 4: $1\sigma$ and $2\sigma$ constraints for $\Lambda$CDM and the T3 and $\text{T3}_\text{ph}$ models in the $(\sigma_8,\Omega_M)$-plane using TT data (left panel) and using all data (right panel). The $1\sigma$-band from SZ clusters and CFHTLenS is shown in dotted green and solid red, respectively. $\Lambda$CDM is in tension with the SZ clusters and CFHTLenS while the T3 and $\text{T3}_\text{ph}$ models are compatible. Even after including the SZ-data, the $2\sigma$$\Lambda$CDM contour does not overlap with the $1\sigma$ SZ contour, which illustrates the tension. On the contrary, the T3 and $\text{T3}_\text{ph}$ contours overlap with the SZ contour.
• Figure 5: $1\sigma$ and $2\sigma$ temperature (TT) constraints in the $(\sigma_8,H_0)$-plane for $\Lambda$CDM and the T3 and $\text{T3}_\text{ph}$ models. The two parameters are uncorrelated in $\Lambda$CDM and $\text{T3}_\text{ph}$ while they are correlated in the T3 model