Probing dark energy dynamics through a new CPL-type $Om(z)$ parametrization in FLRW Universe

Abstract

In this work, we investigate a CPL-type $Om(z)$ parametrization given by $Om(z)=l+m\left(\frac{z}{1+z}\right)$ to study the evolution of dark energy and possible deviations from the standard $\Lambda$CDM cosmology. The model reduces to the flat $\Lambda$CDM scenario for $m=0$, while $m\ne 0$ indicates dynamical evolution. The free parameters are constrained using Pantheon+SH0ES (PPS), Cosmic Chronometer (CC), and DESI BAO DR2 observations through Markov Chain Monte Carlo analysis. The obtained constraints yield $72.48\lesssim H_0\lesssim 72.97\mathrm{km}{\mathrm{s}}^{-1}\mathrm{Mp}{\mathrm{c}}^{-1}$, while the evolution parameter remains negative for all dataset combinations, leading to decreasing $Om(z)$ evolution and favoring quintessence-like behaviour. The combined PPS+CC+DR2 analysis shifts the evolution closer to the $\Lambda$CDM limit. The statistical analysis based on ${\chi }^2$, AIC, and BIC indicates that the proposed model remains statistically competitive with $\Lambda$CDM. The deceleration parameter and total equation of state are further analyzed to examine the cosmic evolution. The transition from deceleration to acceleration occurs within $z_{tr}\approx 0.66-1.01$, while the present values vary within $-0.459\lesssim q_0\lesssim -0.325$ and $-0.639\lesssim {\omega }_0\lesssim -0.550$ depending on the datasets. Overall, the proposed parametrization provides a flexible framework for studying late-time cosmic evolution.

14 pages, 6 figures, and 5 tables. Comments are welcome