Observational Constraints on Quintessence Dark Energy from a Quadratic Deceleration Parametrization

We study the late-time cosmic expansion within a scalar-field dark energy framework in a spatially flat FLRW Universe by adopting a quadratic parametrization of the deceleration parameter [Formula: see text]. This approach allows a controlled and analytical description of the transition from decelerated to accelerated expansion. The model parameters are constrained using MCMC analysis with combined CC, BAO, and standard candle data (SnIa, QSO, GRBs, and [Formula: see text] measurements). The results indicate a transition redshift [Formula: see text] and a present-day value [Formula: see text]. The reconstructed equation-of-state parameter satisfies [Formula: see text], confirming a quintessence-like behavior. The scalar field evolves monotonically, while the reconstructed potential [Formula: see text] remains smooth and exhibits a regular evolution over the considered field range. The model is statistically competitive ([Formula: see text]) and yields [Formula: see text] km s[Formula: see text] Mpc[Formula: see text], highlighting the flexibility of the proposed dynamical dark-energy parametrization and its consistency with current observations. These results support the proposed parametrization as a viable quintessence dark energy scenario consistent with observations.