Vacuum Energy with Natural Bounds: A Spectrally Bounded Effective Explanation​

We propose an observationally motivated effective framework for the gravitationally relevant vacuum sector, in which only a spectrally bounded subset of quantum fluctuations contributes to the vacuum energy density. The construction is defined by two physically motivated scales: a short-wavelength ultraviolet bound associated with confinement-scale physics, and a long-wavelength infrared scale arising from thermodynamic and entropic structuring in the late-time universe. Within this bounded spectral domain, the vacuum energy density is governed by a characteristic geometric scale defined by the ultraviolet and infrared bounds, leading to a robust inverse fourth-power scaling that is largely insensitive to the detailed form of the spectral kernel.This effective description provides a structured interpretation of the observed smallness of vacuum energy in terms of spectral selection rather than ultraviolet cancellation. The model yields testable predictions at low redshift, including percent-level deviations in the equation of state and in the growth of structure, offering a falsifiable alternative to a purely phenomenological cosmological constant.