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 effective infrared reference scale (thermal IR 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-ΛCDM 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 one Python script 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.