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Late-time acceleration with a scalar field source: Observational constraints and statefinder diagnostics

This article discusses a dark energy cosmological model in the standard theory of gravity - general relativity with a broad scalar field as a source. Exact solutions of Einstein's field equations are derived by considering a particular form of deceleration parameter $q$, which shows a smooth transition from decelerated to accelerated phase in the evolution of the universe. The external datasets such as Hubble ($H(z)$) datasets, Supernovae (SN) datasets, and Baryonic Acoustic Oscillation (BAO) datasets are used for constraining the model par parameters appearing in the functional form of $q$. The transition redshift is obtained at $% z_{t}=0.67_{-0.36}^{+0.26}$ for the combined data set ($H(z)+SN+BAO$), where the model shows signature-flipping and is consistent with recent observations. Moreover, the present value of the deceleration parameter comes out to be $q_{0}=-0.50_{-0.11}^{+0.12}$ and the jerk parameter $% j_{0}=-0.98_{-0.02}^{+0.06}$ (close to 1) for the combined datasets, which is compatible as per Planck2018 results. The analysis also constrains the omega value i.e., $Ω_{m_{0}}\leq 0.269$ for the smooth evolution of the scalar field EoS parameter. It is seen that energy density is higher for the effective energy density of the matter field than energy density in the presence of a scalar field. The evolution of the physical and geometrical parameters is discussed in some details with the model parameters' numerical constrained values. Moreover, we have performed the state-finder analysis to investigate the nature of dark energy.