This work presents a minimal effective-field extension of standard cosmology aimed at addressing the Hubble tension, the persistent discrepancy between early- and late-universe measurements of the Hubble constant. We introduce a late-time scalar degree of freedom, Ξ (x^μ), coupled phenomenologically to the matter sector, which modulates the expansion history of the universe. In this framework, the effective Hubble parameter acquires both temporal and weak environmental dependence, allowing distinct observational regimes to infer different values of H₀ without requiring inconsistencies in the underlying cosmological model. The model is formulated at the level of the action, with derived field equations, modified Friedmann equations, and explicit energy-exchange terms between matter and the scalar sector. A dynamical system formulation is developed to analyze the cosmological evolution, including fixed points and late-time attractors. Numerical integration and illustrative expansion histories demonstrate that the scalar-modulated model produces controlled late-time deviations from ΛCDM while preserving early-universe behavior. The resulting expansion history naturally shifts the inferred value of H₀ into the range indicated by local measurements, providing a regime-dependent interpretation of the Hubble tension. The framework remains minimal, testable, and compatible with current observational constraints from Planck, Type Ia supernovae, BAO, and strong-lensing time-delay cosmography. A connection with the broader ToE-2PS (Theory of Everything in Phase Space) program is discussed as a possible theoretical embedding, while all results are derived within a standard effective-field-theory approach. This work provides a coherent and falsifiable late-time cosmological mechanism for reconciling current observational tensions in precision cosmology.
Eduardo Parra (2026) studied this question.