Future CMB cosmological constraints in a dark coupled universe

TL;DR

This paper investigates how a dark matter–dark energy coupling, parameterized by a constant $\xi$, alters future CMB cosmological constraints. The authors modify the background and perturbation equations to include a coupling term $Q^\nu_{(a)}$ with $Q_\nu^{(dm)}=\xi H \rho_{de} u_\nu^{(dm)}$, and they simulate Planck and EPIC data, incorporating gravitational lensing via a minimum-variance quadratic estimator and COSMOMC analysis. They find strong degeneracies between $\xi$ and $\Omega_c h^2$, $\theta_s$, and $H_0$ in primary spectra, causing errors to inflate by up to an order of magnitude relative to the uncoupled case, and that lensing extraction significantly improves EPIC constraints while leaving Planck results largely unchanged due to higher lensing noise. The results demonstrate that CMB lensing is crucial for testing interacting dark energy models with upcoming missions, and EPIC could distinguish coupled from uncoupled cosmologies that appear degenerate with Planck.

Abstract

Cosmic Microwave Background satellite missions as the on-going Planck experiment are expected to provide the strongest constraints on a wide set of cosmological parameters. Those constraints, however, could be weakened when the assumption of a cosmological constant as the dark energy component is removed. Here we show that it will indeed be the case when there exists a coupling among the dark energy and the dark matter fluids. In particular, the expected errors on key parameters as the cold dark matter density and the angular diameter distance at decoupling are significantly larger when a dark coupling is introduced. We show that it will be the case also for future satellite missions as EPIC, unless CMB lensing extraction is performed.

Figures (6)

• Figure 1: Temperature power spectrum signal plus noise for Planck (top panel) and EPIC (bottom panel) experiments. The black curve depicts the $\Lambda$CDM model with $\Omega_{c}h^2= 0.113$. The red curve illustrates a coupled model allowed by Planck data, with $\xi=-0.4$ and $\Omega_{c}h^2= 0.0463$.
• Figure 2: Lensing deflection power spectrum signal plus noise for Planck (top panel) and EPIC (bottom panel) experiments. The black curve depicts the $\Lambda$CDM model with $\Omega_{c}h^2= 0.113$. The red curve illustrates a coupled model allowed by Planck data, with $\xi=-0.4$ and $\Omega_{c}h^2= 0.0463$.
• Figure 3: The panels show the $68 \%$ and $95 \%$ confidence level contours combining the five most correlated parameters ($\Omega_ch^2$, $\theta_s$, $H_0$, $\Omega_\Lambda$ and $\xi$) arising from a fit to mock Planck data without including lensing extraction in the analysis.
• Figure 4: The panels show the $68 \%$ and $95 \%$ confidence level contours combining the five most correlated parameters ($\Omega_ch^2$, $\theta_s$, $H_0$, $\Omega_\Lambda$ and $\xi$) arising from a fit to mock EPIC data without including lensing extraction in the analysis.
• Figure 5: The panels show the $68 \%$ and $95 \%$ confidence level contours combining the five most correlated parameters ($\Omega_ch^2$, $\theta_s$, $H_0$, $\Omega_\Lambda$ and $\xi$) arising from a fit to mock Planck data including lensing extraction in the analysis.