The imprint of the interaction between dark sectors in large scale cosmic microwave background anisotropies

TL;DR

The paper investigates whether interactions between dark energy and dark matter leave measurable imprints on the large-scale CMB, focusing on the late ISW effect. It develops a gauge-invariant perturbation framework with a phenomenological coupling $Q^ u$ and analyzes three coupling forms: proportional to the DE density, DM density, or the total dark-sector density. By performing a joint likelihood analysis with CMB, SNIa, and SDSS data, the authors find that certain couplings are allowed within $1\sigma$, and notably positive energy transfer from DE to DM in the DM- and total-density forms can slow the evolution of the density ratio $r=\rho_c/\rho_d$, helping to alleviate the coincidence problem. The work highlights the ISW signal as a powerful probe of dark sector interactions and motivates future field-theory realizations and improved data to tighten constraints.

Abstract

Dark energy interacting with dark matter is a promising model to solve the cosmic coincidence problem. We study the signature of such interaction on large scale cosmic microwave background (CMB) temperature anisotropies. Based on the detail analysis in perturbation equations of dark energy and dark matter when they are in interaction, we find that the large scale CMB, especially the late Integrated Sachs Wolfe effect, is a useful tool to measure the coupling between dark sectors. We also discuss the possibility to detect the coupling by cross-correlating CMB maps with tracers of the large scale structure. We finally perform the global fitting to constrain the coupling by using the CMB power spectrum data together with other observational data. We find that in the $1σ$ range, the constrained coupling between dark sectors can solve the coincidence problem.

Figures (9)

• Figure 1: The small l CMB angular power spectra when the coupling is proportional to the energy density of DE. The EoS of DE satisfies $w>-1$. The up panel of (d) shows the cross-spectra and the lower panel shows the galaxy power spectra.
• Figure 2: The small l CMB angular power spectra when the coupling is proportional to the energy density of DE. The EoS of DE satisfies $w<-1$.The up panel of (d) shows the cross-spectra and the lower panel shows the galaxy power spectra.
• Figure 3: The irregular behaviors of the small l angular power spectra when the couplings get too negative. Figure (c) indicates the blow up with regard to $\xi_2$ and $w$.
• Figure 4: The small l CMB angular power spectra when the coupling is proportional to the energy density of DM. The DE EoS satisfies $w<-1$. The up panel of (d) shows the cross-spectra and the lower panel shows the galaxy power spectra.
• Figure 5: The small l CMB angular power spectra when the coupling is proportional to the energy density of total dark sectors and the EoS $w<-1$.The up panel of (d) shows the cross-spectra and the lower panel shows the galaxy power spectra.