Searching for dark matter - dark energy interactions: going beyond the conformal case

TL;DR

This study probes a generic interacting dark energy framework in which dark matter and dark energy exchange energy through conformal and disformal couplings, analyzed in conformal, disformal, and mixed variants. The authors derive and solve the background and perturbation equations for an exponential ansatz of the couplings and potential, then confront the models with Planck 2015 CMB data, BAO, SNIa, cosmic chronometers, local H_0, and cluster abundance, using MCMC with CLASS and Monte Python. Growth of structure and lensing data play a crucial role in tightening constraints, with no compelling evidence for DM-DE interactions; conformal coupling bounds reach tight limits around α ≲ 0.03 in several dataset combinations, and disformal couplings are similarly constrained (e.g., D_M ≲ 0.25–0.57 meV^{-1}), while mixed models permit somewhat larger couplings but remain consistent with zero. The results significantly inform the viability of interacting DM-DE scenarios and guide future probes (e.g., 21-cm cosmology, gravitational waves) to further test these couplings.

Abstract

We consider a generic cosmological model which allows for non-gravitational direct couplings between dark matter and dark energy. The distinguishing cosmological features of these couplings can be probed by current cosmological observations, thus enabling us to place constraints on this generic interaction which is composed of the conformal and disformal coupling functions. We perform a global analysis in order to independently constrain the conformal, disformal, and mixed interactions between dark matter and dark energy by combining current data from: Planck observations of the cosmic microwave background radiation anisotropies, a combination of measurements of baryon acoustic oscillations, a supernovae Type Ia sample, a compilation of Hubble parameter measurements estimated from the cosmic chronometers approach, direct measurements of the expansion rate of the Universe today, and a compilation of growth of structure measurements. We find that in these coupled dark energy models, the influence of the local value of the Hubble constant does not significantly alter the inferred constraints when we consider joint analyses that include all cosmological probes. Moreover, the parameter constraints are remarkably improved with the inclusion of the growth of structure data set measurements. We find no compelling evidence for an interaction within the dark sector of the Universe.

Figures (15)

• Figure 1: Cosmological parameter constraints in three coupled DE models with all data set combinations considered in this paper. The coloured intervals correspond to the marginalized $1\sigma$ two--tail limits of each parameter.
• Figure 2: In the upper panel we compare the marginalized constraints on the dimensionless age of the Universe in the conformal, disformal, and mixed coupled DE models using all data set combinations considered in this paper. The lower panel depicts the constraints on $H_\mathrm{astro}t_\mathrm{astro}$ from astrophysical objects refId00004-637X-792-2-1102041-8205-765-1-L12 with their names specified on the vertical axis. In the upper panel the coloured intervals correspond to the inferred $1\sigma$ two--tail limits on the dimensionless age of the Universe, whereas in the lower panel these intervals show the estimated $1\sigma$ constraints.
• Figure 3: Marginalized two--dimensional likelihood constraints for conformally coupled DE with different data set combinations. We show the degeneracy of the conformal coupling parameter $\alpha$ with $\lambda,\,\Omega_m,\,\sigma_8,$ and $H_0$.
• Figure 4: Marginalized one--dimensional posterior distributions for the conformal coupling parameter $\alpha$, with the different data set combinations indicated in the figure. The respective parameter constraints are tabulated in Table \ref{['table:conf_Tab1']}.
• Figure 5: Marginalized two--dimensional likelihood constraints on the parameters $\alpha,\,\lambda,\,\Omega_m,\,\sigma_8,$ and $H_0$ in the conformal model. The respective parameter constraints are tabulated in Table \ref{['table:conf_Tab2']}.