Nonminimally Coupled Quintessence with Double Exponential Potential: Observational Evidence Against Big Crunch Singularity

Abstract

We investigate a class of scalar field dark energy models non-minimally coupled to gravity, characterized by a double exponential potential and parameterized coupling $\xi$. We study the cosmological dynamics for a recently proposed descending dark energy model, namely, Q-SC-CDM. Initially, we choose distinct values of coupling parameter. For some values of $\xi$, the evolution of the universe is split up into three different phases: {\it decelerated expansion (early time), accelerated expansion (late-time) and slow-contraction (future era)}, and provide Big Crunch Singularity at distant future. In other scenario, the phase of slow-contraction vanishes, cosmic acceleration is obtained at current epoch, and the universe gets de-Sitter expansion at distant future. We confront the model with various datasets, including Cosmic Chronometers, Type Ia Supernovae (Pantheon+, DES, and Union 3), and Baryon Acoustic Oscillation measurements from DESI. Our analysis reveals that observational constraints naturally favor regions of parameter space in which the model avoids future singularities and slow-contraction phases, even for relatively small values of $\xi \simeq 0.12$. The preferred solutions yield values of $\Omega_{m}$, $H_0$, and $r_d$ that are consistent with those of $\Lambda$CDM at the $68\%$ confidence level. In contrast, the models with fixed couplings $\xi=0.3$ and $\xi=0.5$, which predict $H_0>70$ km/s/Mpc, are strongly disfavored relative to $\Lambda$CDM by the current datasets. Finally, the phase-space analysis confirms that the observationally constrained model with $\xi\simeq 0.12$ evolves toward a stable de Sitter attractor.