Future weak lensing constraints in a dark coupled universe

TL;DR

The paper investigates a dark sector coupling between dark matter and dark energy, parameterized by the dimensionless constant $ξ$, and assesses how future Planck data combined with Euclid or LSST-like weak lensing surveys can constrain this interaction. By modifying CAMB to include the coupling and performing MCMC forecasts that combine CMB lensing with tomographic weak lensing, the authors find that $ξ$ can be limited to roughly $ξ> -0.04$ (Planck+Euclid) at 95% c.l., with LSST providing similar bounds; however, $ξ$ remains strongly degenerate with $H_0$ and $Ω_c h^2$, potentially biasing other parameters if the coupling is ignored. The study also demonstrates that neglecting a nonzero $ξ$ can bias cosmological inferences, underscoring the need to consider coupled dark sector models in high-precision cosmology and to model non-linear scales for robust constraints. These results highlight the value of combining CMB lensing with weak lensing tomography to probe dark energy–dark matter interactions and motivate further work on non-linear and cluster-scale signatures of coupled cosmologies.

Abstract

Coupled cosmologies can predict values for the cosmological parameters at low redshifts which may differ substantially from the parameters values within non-interacting cosmologies. Therefore, low redshift probes, as the growth of structure and the dark matter distribution via galaxy and weak lensing surveys constitute a unique tool to constrain interacting dark sector models. We focus here on weak lensing forecasts from future Euclid and LSST-like surveys combined with the ongoing Planck cosmic microwave background experiment. We find that these future data could constrain the dimensionless coupling to be smaller than a few $\times 10^{-2}$. The coupling parameter $ξ$ is strongly degenerate with the cold dark matter energy density $Ω_{c}h^2$ and the Hubble constant $H_0$.These degeneracies may cause important biases in the cosmological parameter values if in the universe there exists an interaction among the dark matter and dark energy sectors.

Figures (5)

• Figure 1: 2-D constraints on $\xi$ and $\Omega_m$ using Planck and LSST data (blue contours) and Planck and Euclid data (red contours).
• Figure 2: 2-D constraints on $\xi$ and $\Omega_m$ using Planck (blue contours) and Planck plus Euclid (red contours).
• Figure 3: Top panel: $68\%$ and $95 \%$ c.l. contours in the ($\Omega_m$, $\xi$) plane from Planck data only. Bottom panel: same as in the top panel, but for the combination of Planck plus Euclid data (note the different scale for the x-axis).
• Figure 4: Top panel: $68\%$ and $95 \%$ c.l. contours in the ($H_0$, $\xi$) plane from Planck data only. Bottom panel: same as in the top panel, but for the combination of Planck plus Euclid data (note the different scale for the x-axis).
• Figure 5: $68\%$ and $95 \%$ confidence levels from Planck plus Euclid data when a fiducial cosmology with $\xi=-0.1$ is fitted to a non interacting cosmology with $\xi$ fixed to $0$ (blue countours) or to an interacting cosmology in which $\xi$ is allowed to vary.