Cosmic Irreversibility under Universal Operator Grammar: A Phenomenological Framework for Dynamical Dark Energy and Growth Suppression

The standard ΛCDM model provides an excellent phenomenological description of cosmic expansion but leaves open the physical origin of Λ, the coincidence problem, and the persistent tension between early‑ and late‑universe estimates of structure growth. This work presents a UOG‑compatible phenomenological model in which late‑time cosmic acceleration is interpreted as the geometric projection of irreversible work associated with structure formation. An effective irreversibility fraction ε(a) is introduced and treated as a constitutive function, with the effective dark‑energy density modeled as ρ_DE,eff(a) = α ρ_m(a) ε(a). A second constitutive coupling modifies the growth response through G_growth(a) = G[1 + α ε(a)(1 + b₀ ε(a))]. The central falsifiable requirement is that the same ε(a) must jointly determine both the expansion history and the growth suppression. This paper does not claim a fundamental derivation of ε(a) from a UOG action; instead, it provides a structured phenomenological framework with clear observational tests and a well‑defined path toward a future action‑based formulation.