Principles of Cosmological Dynamics - Volume I: An Expansion Model from Fluid Coupling and Radiative Interaction

Principles of Cosmological Dynamics – Volume I This preprint presents a theoretical model of cosmological expansion based on a radiative coupling between the cosmological radiation and a background continuum (Æther D). The model interprets the cosmological redshift as a physical energy-transfer process governed by a minimal coupling law, leading to the emergence of a negative-pressure component capable of contributing to the late-time expansion of the Universe. The manuscript develops the model from its axioms, establishes the coupled continuity equations, formalises the conservation framework, and obtains analytical solutions describing the cosmological dynamics. The interaction law is derived as the minimal form compatible with the hypotheses of locality, dimensional consistency, and the absence of any additional physical scale, with its single parameter bounded as a capture efficiency. The blackbody spectrum of the cosmological radiation is preserved by construction, and the entropy budget of the coupling is established. The observational consequences of the model are discussed, including the evolution of the cosmological radiation temperature T(z), the effective equation of state, and a correlated violation of the Etherington distance-duality relation — three signatures capable of distinguishing the model from the standard ΛCDM framework. This first volume is exclusively devoted to the dynamics of cosmological expansion; developments concerning emergent gravitation and the microstructure of spacetime will be the subject of a subsequent volume. This is the English edition of the work. The original French edition is available at: https://doi.org/10.5281/zenodo.21308448