Late-Time Cosmic Acceleration from QCD Confinement Dynamics

Abstract: We explore a phenomenological extension of the Polyakov-Nambu-Jona-Lasinio (PNJL) model by introducing a coupling between the Polyakov loop potential and the Hubble parameter $H(t)$, inspired by the hypothesis that the QCD vacuum, particularly in the confined phase, may be sensitive to the large-scale dynamics of the universe. The coupling term, proportional to $(H(t)/H_0)^d f(\Phi)$, vanishes in the deconfined regime and acts as a dynamical dark energy contribution at late times, without invoking a fundamental cosmological constant. This framework maintains the thermodynamic consistency of the PNJL model and introduces a minimal modification to the effective potential, controlled by a single exponent $d$. We confront the model with low-redshift cosmological data, including cosmic chronometers, Type Ia supernovae, HII galaxies, and quasars. Using a Bayesian Monte Carlo analysis, we derive constraints on the model parameters and compare its performance with LambdaCDM. Our results show that the modified PNJL cosmology provides a statistically competitive fit to current data within 68% C.L.; while offering a theoretically motivated alternative to standard dark energy scenarios. We discuss the implications for QCD in curved spacetime and suggest avenues for further theoretical and observational investigation.