SSFDE Model: Cosmological Implications and Dynamical System Analysis

TL;DR

This work investigates an interacting scalar field dark energy model with an exponential potential and a dark-sector coupling $Q=3\gamma H\rho_{dm}$, tested against DESI DR2 BAO, Pantheon+ SNe, and compressed CMB data. The authors constrain background evolution and perform a dynamical-systems analysis, revealing five interacting and four non-interacting critical points that trace cosmic history from early stiff/matter-like stages to late-time acceleration; stability regions in the $(\lambda,\gamma)$ plane govern the viability of attractors. Observationally, the interacting model yields $h=0.659\pm0.0063$ with $\gamma>0$ favored, and Bayes factor $|\Delta\ln Z|\approx5.0$, indicating moderate-to-strong evidence against $\Lambda$CDM in this dataset combination, while the non-interacting case remains inconclusive. The dynamical analysis shows that the interaction introduces new stable accelerated attractors and shifts the phase-space structure, enabling a graceful transition to acceleration without ghosts or early instabilities, and potentially alleviating late-time tension in $H_0$ and $r_d$. Overall, SSFDE with dark-sector coupling emerges as a dynamically viable and observationally competitive extension of $\Lambda$CDM.

Abstract

In this paper, we consider an interacting scalar field dark energy model with an exponential potential and a dark sector coupling \( Q = 3γHρ_{dm} \), which has been observationally tested using recent baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2 , Unanchored Type Ia Supernovae, and the compressed CMB likelihood. We find that the Interacting model predicts a Hubble constant of $h = 0.659 \pm 0.0063$, deviating from the $Λ$CDM value by approximately $2.93σ$, while the Non-Interacting model shows a $3.78σ$ deviation. The positive coupling parameter (\( γ> 0 \)) further suggests a transfer of energy from dark matter to dark energy. According to the Jeffreys scale, the Interacting model shows moderate evidence against the $Λ$CDM model, whereas the Non-Interacting model shows only inconclusive evidence. Further, we investigate both models through the lens of dynamical systems analysis. We formulate the cosmological evolution equations with a phenomenological interaction term and recast them into an autonomous system to study the qualitative behavior of cosmic expansion. Critical points of the system are identified and analyzed to study the corresponding cosmological dynamics. In the interacting model, we obtained five critical points, whereas in the non-interacting scenario, four distinct sets of critical points were identified. The obtained critical points, governed by cosmological parameters, represent distinct cosmic epochs, commencing from the early time stiff matter domination to late-time acceleration. Their stability is examined through linear stability analysis under appropriate physical constraints. The evolution of background cosmological parameters are also examined in terms of the dynamical system variable, and the obtained values align with observational results.

Figures (6)

• Figure 1: The figure shows confidence contours at the 1$\sigma$ and 2$\sigma$ levels, based on constraints for the Non-Interacting, Interacting, and $\Lambda$CDM Models, model
• Figure 2: Region in $\left(\lambda,\gamma\right)$ space,where $A_{3\pm}$ exhibits stable behavior
• Figure 3: Region plot in $\lambda -\gamma$ parameter space corresponding to critical points $A_{5\pm}$
• Figure 4: The numerical solutions of the equation \ref{['eq30']}-\ref{['eq32']} describing the density parameters ($\Omega_{dm}$ and $\Omega_\phi$) and the Eos parameter ($\omega_{tot}$) together with the deceleration parameter (q) are presented. The vertical line $N = 0$ represents the current timeline, and $N > 0$ and $N < 0$ represent the future and past epochs, respectively.
• Figure 5: The numerical solutions of \ref{['eq43']}, \ref{['eq44']} and \ref{['eq45']} describing the density parameters and the Eos parameter ($\omega_{eff}$) together with the deceleration parameter (q) are presented. The vertical line N = 0 represents the current timeline, and N $>$ 0 and N $<$ 0 represent the future and past epochs, respectively.