Consequences of dark matter-dark energy interaction on cosmological parameters derived from SNIa data

TL;DR

This paper examines a phenomenological dark-energy–dark-matter coupling characterized by a constant $\delta$, which yields $\rho_{DM}(a)=\rho_{DM}^{(0)}a^{-3+\delta}$ and modifies the DE continuity equation. By parameterizing the DE EOS as $w_{DE}(z)=w_0+w_1 z$ and deriving the analytic luminosity distance $d_h(z)$ for a flat universe, the authors fit SNIa data from the gold and SNLS samples to assess how the coupling affects $w_{DE}(z)$ and $\Omega_{DM}^{(0)}$, and compare with the CMB shift parameter $R$. They find that nonzero $\delta$ tends to push the inferred $\Omega_{DM}^{(0)}$ upward and increases tension with CMB observations, with the effect persisting under a varying $w_{DE}$ but mitigated when priors on $\Omega_{DM}^{(0)}$ are included. The results underscore the importance of combining SNIa with CMB and independent $\Omega_{DM}^{(0)}$ measurements to constrain interacting-dark-energy models and to avoid biased inferences about DE dynamics.

Abstract

Models where the dark matter component of the universe interacts with the dark energy field have been proposed as a solution to the cosmic coincidence problem, since in the attractor regime both dark energy and dark matter scale in the same way. In these models the mass of the cold dark matter particles is a function of the dark energy field responsible for the present acceleration of the universe, and different scenarios can be parameterized by how the mass of the cold dark matter particles evolves with time. In this article we study the impact of a constant coupling $δ$ between dark energy and dark matter on the determination of a redshift dependent dark energy equation of state $w_{DE}(z)$ and on the dark matter density today from SNIa data. We derive an analytical expression for the luminosity distance in this case. In particular, we show that the presence of such a coupling increases the tension between the cosmic microwave background data from the analysis of the shift parameter in models with constant $w_{DE}$ and SNIa data for realistic values of the present dark matter density fraction. Thus, an independent measurement of the present dark matter density can place constraints on models with interacting dark energy.

Figures (6)

• Figure 1: Countour plots in the $w_{0}-\Omega_{DM}$ plane for a constant equation of state with 68% confidence level for different values of the DM-DE coupling $\delta$ ($\delta=0$ (dotted line), $\delta=0.2$ (dashed line), and $\delta=0.6$ (solid line)). The best fit values are marked by an "$\ast$' ($\delta=0$), "+' ($\delta=0.2$) and an "X' ($\delta=0.6$), using the gold SNIa (left figure) and SNLS (right figure) data.
• Figure 2: Countour plots in the $w_{0}-\Omega_{DM}$ plane for a constant equation of state with $3 \sigma$ confidence level for different values of the DM-DE coupling $\delta$. We compare constraints from the gold data set SNIa (solid line) and CMB (dashed line) data.
• Figure 3: Countour plots in the $w_{0}-\Omega_{DM}$ plane for a constant equation of state with $3 \sigma$ confidence level for different values of the DM-DE coupling $\delta$. We compare constraints from the SNLS SNIa (solid line) and CMB (dashed line) data.
• Figure 4: Countour plots in the $w_{0}-\Omega_{DM}$ plane marginalized over values of $w_{1}$ with 68% confidence level for different values of the DM-DE coupling $\delta$ ($\delta=0$ (dotted line), $\delta=0.2$ (dashed line), and $\delta=0.6$ (solid line)). The best fit values are marked by an "$\ast$' ($\delta=0$), "+' ($\delta=0.2$) and an "X' ($\delta=0.6$), using the gold SNIa (left figure) and SNLS (right figure) data.
• Figure 5: Plot of the likelihood function for $\Omega_{DM}$ with $w_{0}$ and $w_{1}$ marginalized for different values of the DM-DE coupling $\delta$ ($\delta=0$ (dotted line), $\delta=0.2$ (dashed line), and $\delta=0.6$ (solid line)) using the gold SNIa (left figure) and SNLS (right figure) data.