Late-time cosmic acceleration in torsion-free f(Q) gravity: Dynamical and thermodynamical analysis

We investigate the late-time dynamics of cosmic expansion within a torsion-free formulation of f ( Q ) gravity in a spatially flat Friedmann-Robertson-Walker universe. Adopting a specific non-metricity model that reduces to standard cosmology at early times, we explore whether accelerated expansion can emerge purely from geometric effects without introducing a cosmological constant. To probe the dynamical behavior of dark energy, three redshift-dependent parameterizations of the equation of state are considered. The resulting cosmological evolution is analyzed through a comprehensive set of diagnostics, including the effective equation of state, deceleration parameter, O m diagnostic and higher-order cosmographic quantities such as the jerk, lerk, and time parameter. These indicators consistently reveal a transition from decelerated to accelerated expansion and demonstrate clear deviations from the standard ΛCDM scenario, highlighting the dynamical nature of the underlying models. Furthermore, the thermodynamical viability of the framework is examined by testing the generalized second law of thermodynamics, Gibbs free energy ( G ) and heat capacity C . The positivity of the total entropy variation throughout the relevant redshift range confirms the thermodynamic consistency of the models. Moreover, the thermodynamical stability of the system is also confirmed by obtaining C > 0 and G < 0.

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