Hybrid 5D Gravity (H5DG): A Step Towards Unification

This record contains the complete sixteen-paper corpus of Hybrid 5D Gravity (H5DG), assembled as a single ordered reference edition. H5DG investigates how far a single-boundary five-dimensional braneworld can provide a unified framework for gravitational phenomenology, from the Solar System to cosmology, while remaining as close as possible to five-dimensional Einstein gravity. The matter sector is deliberately not derived from the gravitational action. The corpus is arranged according to its logical dependencies. Part I establishes the fundamental action, geometry, scope and residual brane-location modulus. Part II develops the spin-zero, vector, gravitational-slip and preferred-frame sectors. Part III states the binding Solar–Galactic domain rule and introduces the filtered effective completion. Parts IV and V apply the resulting framework to infrared phenomenology, the radial acceleration relation, scalar fluctuations, the coupled metric–aether sector, compact-object dark matter and the Bullet Cluster. Part VI treats Big-Bang nucleosynthesis and cosmology. Part VII presents a deliberately conservative extension beyond the baseline gravitational theory. The Q2 domain-rule paper is placed before all subsequent AQUAL applications. It establishes that the local AQUAL equation used throughout the phenomenological papers is the long-wavelength and galactic limit of a domain-matched filtered brane response, rather than a universal Solar–Galactic field equation. This ordering makes the scope of the later applications explicit while leaving their results within the stated domain unchanged. A further scope result, stated in Section 1 of the opening paper, applies throughout. After matching the four-dimensional Newton constant and the AdS curvature radius, the local junction condition, homogeneous Friedmann equation, thermal emissivity and radial bulk evolution equations of H5DG are identical to those of Randall–Sundrum II. Local RS2-equivalent equations are accordingly not counted within the corpus as independent H5DG distinctiveness; the theory's specific content lies in the finite cavity, the cap and horizon prescription, and the non-radial transport and late-time matching problems. The corpus distinguishes between results derived from the minimal five-dimensional action, effective completions adopted at brane level, phenomenological inputs, numerical benchmarks and unresolved microscopic closure questions. Results are labelled throughout as established (†), derived here (‡), conditional (§), or open (¶). Among the open items are the microscopic origin of the Solar–Galactic matching length, the merger-capable fraction of the compact-object sector, which is underdetermined by the present action, and the late-time bulk matching problem following a radiating epoch. The corpus should therefore be read as a structured theoretical research programme rather than as a claim that every sector has already been derived uniquely from the minimal action. The unified edition includes a dedicated corpus contents section, PDF bookmarks and continuous corpus pagination from page 1 through page 375. The individual papers retain their original titles and internal section, equation, figure, table and reference numbering, allowing them to be read and cited either separately or as components of the complete H5DG corpus.