A Phenomenological Modeling of Mildly Dynamic Dark Energy Within a Minimal, Epoch Dependent Framework

Dark energy is described in the standard cosmological model as a strictly constant component with an equation of state fixed at . While this assumption is mathematically simple and observationally viable, it is not strictly required by current data. Recent large‑scale surveys — including BAO measurements, supernova observations, and combined late‑time analyses with CMB information — have shown that a mildly dynamic form of dark energy remains observationally allowed and may even provide a slightly improved fit in certain regimes. This paper develops a minimal phenomenological framework in which dark energy exhibits an extremely low‑frequency temporal modulation. The approach remains fully compatible with ΛCDM in the limit of vanishing dynamics and avoids any microphysical assumptions. The conceptual motivation is inspired by the Frequency‑Energy‑Resonance Theory (FERT), which interprets background terms as long‑wavelength resonance modes. The proposed parametrization is deliberately conservative, empirically testable, and formulated with explicit falsification criteria.