Vacuum Gravitation and the Irreversible Sector: A Phenomenological Proposal

The cosmological constant problem persists because all standard approaches assume that vacuum energy couples to spacetime curvature via its magnitude. This paper proposes that the coupling assumption itself may be incomplete: if the vacuum possesses an irreducible irreversible sector alongside its energetic content, then the geometrically relevant quantity need not be the magnitude of the vacuum's zero-point contributions but the derivative structure of a phenomenological residue field R. Physics already admits rigorously structured systems in which reversible and irreversible contributions are generated by distinct operators subject to mutual degeneracy constraints; the GENERIC formalism provides the established example. The present paper does not claim the quantum vacuum is a GENERIC system. It proposes, by analogy with that formal precedent, that vacuum gravitation may be mis-specified because physics has conflated sector magnitude with geometrically relevant derivative structure. We introduce R as a phenomenological scalar field and couple its Hessian to the Einstein tensor. The trace of the modified equation yields a scalar curvature contribution proportional to the d'Alembertian of R, which is naturally small in a homogeneous universe regardless of the magnitude of R. The Bianchi identity yields a consistency condition for R involving a Ricci-tensor correction. The framework predicts deviation from strictly constant dark energy, consistent with DESI DR2 results. A provisional effective action is sketched from which the field equation can in principle be derived.