An analytic model for interacting dark energy and its observational constraints

TL;DR

<3-5 sentence high-level summary goes here with math: The paper proposes a phenomenological, non-gravitational interaction between dark energy and cold dark matter in a flat FLRW universe, specified by $Q = 3\\lambda_m H \\rho_m + 3\\lambda_d H \\rho_d$, and derives analytic solutions for both constant and variable dark-energy EoS. It analyzes the asymptotic behavior, showing that very small couplings recover $\\Lambda$CDM or, for larger couplings, can yield phantom behavior; it constrains the model using 194 Type Ia SN data and explores cosmography with statefinders and higher-order parameters, finding results compatible with observational data and Planck. The work demonstrates that an interacting DE framework can mimic $\\Lambda$CDM in the late universe and remains a viable alternative, with clear predictions for the evolution of $\\omega_d$, density parameters, and the deceleration parameter $q$, and suggests future extensions to include baryons and radiation.

Abstract

The paper deals with a theoretical model for interacting dark energy. The interaction between the cold dark matter (dust) and the dark energy has been assumed to be non-gravitational in nature. Exact analytic cosmological solutions are obtained both for constant and variable equation of state for dark energy. It is found that, for very small value of the coupling parameter (in the interaction term), the model asymptotically extends up to $Λ$CDM, while the model can enter into the phantom domain asymptotically, if the coupling parameter is not so small. Both the solutions are then analyzed with 194 Supernovae Type Ia data. The best fit parameters are shown with 1$σ$ and 2$σ$ confidence intervals. Finally, we have discussed the cosmographic parameters for both the cases.

Figures (7)

• Figure 1: The figure shows the behavior of the variable $\omega_d$ throughout the entire evolution of the universe.
• Figure 2: This shows that in high redshift era, $\omega_d$ was still negative.
• Figure 3: The observed 194 Hubble free luminosity distance and the theoretically predicted luminosity distance (continuous graph) for $\omega$CDM (where $\omega= -1.01$) have been shown.
• Figure 4: 68% ($1\sigma$) and 95% ($2\sigma$) confidence level contours in ($\Omega_{m0}, \Omega_{d0}$), ($\Omega_{m0}, \omega_{d0}$) and ($\Omega_{d0}, \omega_{d0}$) plane have been shown with the best fit parameter indicated by the black dot in each plot.
• Figure 5: The $1\sigma$ and $2\sigma$ confidence levels in the ($\Omega_{m0}, \Omega_{d0}$) plane have been shown for $n= 0.8$, $n= 0.9$, and $n= 1.1$ respectively in the clockwise direction. The best fit values of ($\Omega_{m0}, \Omega_{d0}$) for different $n$ have also been indicated by the black dot in each figure.