Vacuum Energy with Natural Bounds: A Spectral Approach without Fine-Tuning

The cosmological constant problem remains one of the deepest challenges in theoretical physics, with a discrepancy of over 120 orders of magnitude between quantum field theory and observational cosmology. This paper presents the \textbf{QEV model} (Quantum Energy Vacuum model), a novel spectral approach that circumvents the need for fine-tuning by applying natural physical bounds to vacuum energy. The model proposes a spectrally bounded integration defined by two empirically grounded limits: the QCD confinement scale as an upper bound and a thermodynamic suppression below approximately 30\,K as a lower bound. This double-bound structure, governed by a double exponential damping function, yields a consistent and convergent estimate of the vacuum energy density. It further provides a unified explanation for both the observed cosmic acceleration and galactic rotation curves, thereby connecting dark energy and dark matter to the structure of the vacuum itself. The model additionally interprets the QCD phase boundary as an informational horizon, reinforcing its phenomenological and epistemic coherence.