Dark sectors with dynamical coupling

TL;DR

This work investigates a time-dependent coupling between dark matter and dark energy, parameterized by $ξ(a)=ξ_0+ξ_a(1-a)$, within two interacting vacuum models IVS1 and IVS2. Using Planck 2015 CMB data together with BAO, Pantheon, and Riess $H_0$ priors, the authors constrain an eight-parameter cosmology and compute Bayesian evidences relative to ΛCDM. They find a strong anti-correlation between the coupling parameters $ξ_0$ and $ξ_a$, with $(ξ_0,ξ_a)=(0,0)$ typically consistent, and while CMB-only data can suggest a positive coupling at some epochs and modestly ease the $H_0$ tension, overall Bayesian analysis does not favor dynamical coupling over ΛCDM. The results indicate that a redshift-dependent dark sector interaction remains a permitted extension that can mitigate certain cosmological tensions, but it is not yet statistically preferred given current data. $ξ(a)$ remains a key descriptor of potential new physics in the dark sector, warranting tighter observational constraints.

Abstract

Coupled dark matter-dark energy scenarios are modeled via a dimensionless parameter $ξ$, which controls the strength of their interaction. While this coupling is commonly assumed to be constant, there is no underlying physical law or symmetry that forbids a time-dependent $ξ$ parameter. The most general and complete interacting scenarios between the two dark sectors should therefore allow for such a possibility, and it is the main purpose of this study to constrain two possible and well-motivated coupled cosmologies by means of the most recent and accurate early and late-time universe observations. We find that CMB data alone prefers $ξ(z) >0$ and therefore a smaller amount of dark matter, alleviating some crucial and well-known cosmological data tensions. An objective assessment of the Bayesian evidence for the coupled models explored here shows no particular preference for the presence of a dynamical dark sector coupling.

Figures (6)

• Figure 1: Two-dimensional contours and one-dimensional marginalized posterior distributions for some key parameters of the IVS1 scenario for the CMB and CMB+R19 data sets.
• Figure 2: Two-dimensional contours and one-dimensional marginalized posterior distributions for some key parameters of the IVS1 scenario for the CMB+BAO and CMB+BAO+R19 data sets.
• Figure 3: Redshift evolution of the dynamical coupling parameter $\xi (z)$ ($1+z = a^{-1}$) for the IVS1 scenario using various observational datasets. The left panel corresponds to the CMB and CMB+R19 datasets while the right panel stands for the CMB+BAO and CMB+BAO+R19.
• Figure 4: Two-dimensional contours and one-dimensional marginalized posterior distributions for some key parameters of the IVS2 scenario for the CMB and CMB+R19 data sets.
• Figure 5: Two-dimensional contours and one-dimensional marginalized posterior distributions for some key parameters of the IVS2 scenario for the CMB+BAO and CMB+BAO+R19 data sets.