Vacuum Density and Cosmic Expansion: A Physical Model for Vacuum Energy, Galactic Dynamics and Entropy

We introduce a Quantum Entropic Vacuum (QEV) framework in which the vacuum spectrum is bounded by a QCD-scale ultraviolet knee and a thermal infrared floor anchored to the CMB Wien scale. At galaxy scales, this bounded spectrum maps to four interpretable contributions—Newtonian (baryonic), a mid-disk thermal lift, a saturating entropic term, and a sign-definite hadronic floor modeled as a weak negative acceleration. Using a single, unit-consistent configuration, we reproduce the rotation curve of NGC~3198 with small residuals and illustrate, on a few additional spirals, that flat outer regions can emerge in the shown cases without explicitly adding dark halos. At background level, diagnostic panels for \( E(z) \) and \( q(z) \) broadly track flat-\( \Lambda \)CDM for \( \)\( \)0 < z ≲ 1. These cosmology curves are illustrative only; we do not perform a joint likelihood over SNe~Ia, BAO, or cosmic-chronometer data in this work. For transparent figure-level replication, we provide a minimal package consisting of two Python scripts and two small SPARC-based tables (CSV). The present results should be read as an indication of how the QEV picture can operate in practice, motivating targeted observational tests and a full statistical validation in follow-up work.