Astronomical bounds on a cosmological model allowing a general interaction in the dark sector

TL;DR

The paper develops and tests a general linear interaction model between cold dark matter and dark energy in a flat FLRW universe with constant DE equation of state. It analytically solves the background evolution, yielding $ ho_t(z)=\rho_1(1+z)^{r_1}+\rho_2(1+z)^{r_2}$ with $r_1,r_2$ determined by the coupling constants, and expresses $H(z)$, $\rho_m(z)$, and $\rho_d(z)$ in closed form. By fitting to low-redshift data from SNe (JLA) and Hubble parameter measurements for three DE scenarios (quintessence, vacuum, phantom), the study constrains the coupling parameters, shows ΛCDM is still viable at 1σ, and reveals possible sign changes in the energy transfer $Q$ for some couplings. The work also employs cosmographic and Om diagnostics, and thermodynamic arguments based on the apparent horizon to assess model viability, finding that positive $r_2$ values are favored and that generalized second law holds. Overall, while ΛCDM remains a good fit, the generalized interacting dark sector can reproduce late-time acceleration with nuanced deviations and provides a framework for richer dark-energy phenomenology without strong favoritism toward any fixed DE equation of state.

Abstract

Non-gravitational interaction between two barotropic dark fluids, namely the pressureless dust and the dark energy in a spatially flat Friedmann-Lemaître-Robertson-Walker model has been discussed. It is shown that for the interactions which are linear in terms the energy densities of the dark components and their first order derivatives, the net energy density is governed by a second order differential equation with constant coefficients. Taking a generalized interaction, which includes a number of already known interactions as special cases, the dynamics of the universe is described for three types of the dark energy equation of state, namely that of interacting quintessence, interacting vacuum energy density and interacting phantom. The models have been constrained using the standard cosmological probes, Supernovae type Ia data from joint light curve analysis and the observational Hubble parameter data. Two geometric tests, the cosmographic studies and the $Om$ diagnostic have been invoked so as to ascertain the behaviour of the present model vis-a-vis the $Λ$-cold dark matter model. We further discussed the interacting scenarios taking into account the thermodynamic considerations.

Figures (14)

• Figure 1: $1\sigma$ ($68.3\%$), $2\sigma$ ($95.4\%$) and $3\sigma$ ($99.7\%$) confidence level contour plots for the model parameters of the interacting quintessence dark energy, in particular for $w_{d}=- \, 0.98$, have been shown using the observational data OHD$+$SNe. Additionally, the figure also shows the one dimensional marginalised posteriors distributions for the parameters ($\Omega_{d0}$, $r_1$, $r_2$).
• Figure 2: The plots for deceleration parameter $q$ (upper panel) and the total equation of state $w_{tot}$ (lower panel) in the interacting scenario when dark energy is of quintessence type, have been shown using the observational data OHD$+$SNe. In both panels we have shown the 1$\sigma$ ($68.3\%$) and 2$\sigma$ ($95.4\%$) confidence regions around the best fit curve (the central dark line).
• Figure 3: $1\sigma$ ($68.3\%$), $2\sigma$ ($95.4\%$) and $3\sigma$ ($99.7\%$) confidence level contour plots for the model parameters of the interacting cosmological constant (i.e. $w_d= -\,1$) using the observational data OHD$+$SNe. Additionally, the figure also displays the one dimensional marginalised posteriors distributions of the parameters for the parameters ($\Omega_{d0}$, $r_1$, $r_2$).
• Figure 4: The plots for the deceleration parameter $q$ (upper panel) and the total equation of state $w_{tot}$ (lower panel) in the interacting scenario when dark energy is the cosmological constant itself, have been shown using the observational data OHD$+$SNe. In both panels we have shown the 1$\sigma$ ($68.3\%$) and 2$\sigma$ ($95.4\%$) confidence regions around the best fit curve (the central dark line).
• Figure 5: $1\sigma$ ($68.3\%$), $2\sigma$ ($95.4\%$) and $3\sigma$ ($99.7\%$) confidence level contour plots for the model parameters of the present interacting phantom dark energy, in particular for $w_{d}=-1.02$, have been shown using the observational data OHD$+$SNe. Additionally, the figure also shows the one dimensional marginalised posteriors distributions for the parameters ($\Omega_{d0}$, $r_1$, $r_2$).