We present the Resonance Space-Time Expansion Model (RSEM), a covariant scalar-field framework intended to replace the dark sector with a single resonance field. The model is formulated as a regulated P (X) -type theory that interpolates between a dust-like clustering regime at early times and a late-time accelerating phase. In the weak-field limit, RSEM yields a modified Poisson equation that reproduces flat galactic rotation curves and the baryonic Tully-Fisher relation, while reducing to Newtonian and General Relativistic behaviour in the high-acceleration regime. Within the cosmological background, the model admits a unified description in which the same field can behave approximately as pressureless matter at recombination and as a dark-energy-like component at late times. RSEM further proposes an internal link between the galactic acceleration scale a_ and the Hubble scale H₀, providing a model-based explanation for their observed proximity. We derive the covariant field equations, state the stability and consistency conditions for the intended branch, and outline observational consequences relevant to structure growth, lensing, and late-time expansion. Several phenomenological consequences, including the detailed matter power spectrum, cluster-merger lensing morphology, and precision confrontation with cosmological datasets, remain to be established through dedicated numerical implementation.
Erin Byers (Sun,) studied this question.