Gravity, Electromagnetism, and the Dark Sector from a Single Displacement Action with Zero Free Parameters

We present a classical unified field theory in which gravity, electromagnetism, and a displacement scalar field D interact through a single covariant action built on an Energy–Space–Displacement (ESD) framework. The displacement medium couples conformally to matter, kinetically to geometry, and gauge-kinetically to electromagnetism, bridging the three sectors without modifying general relativity or Maxwell theory on their tested domains. In the static weak-field limit the unified action yields a parameterless low-acceleration closure whose every constant is built from the golden ratio φ = (1+√5)/2 and its logarithm: Δg · (u^φ + (φ⁶−2)·u^(2lnφ/φ) + (4lnφ−1)/φ) = (16φ+1)·gN, u ≡ 4gN/a₀. A self-consistency condition on the kinetic screening—requiring that the product of the screening exponent and the maximum gradient instability equal unity—uniquely fixes the primary exponent p = φ; three algebraic identities then reduce five closure constants to two. The kinetic function governing the displacement medium is thereby uniquely determined, yielding a complete covariant field system with zero continuously-free parameters in the gravitational sector; the sole discrete choice—the E-channel amplitude b = φ⁶ − 2—is selected from a four-element Fibonacci-ring landscape as the unique value compatible with observation. Tested against 171 SPARC galaxies (3,375 data points), the closure achieves 53 wins, 94 ties, and 24 losses versus MOND, with a total Δχ² = −843; nuisance-sensitivity testing reduces losses to 5 at 1σ and 1 at 2σ. The three denominator terms of the screening function map one-to-one onto the Displacement, Energy, and Space sectors of the action, providing a direct observational fingerprint of the ESD unification. Gravitational waves propagate at exactly c (consistent with GW170817), solar-system PPN constraints are satisfied with |γ−1| ~ 10⁻⁹, and the oscillating D-field reproduces ΛCDM at both background and linear-perturbation levels. The framework does not yet address non-abelian gauge groups or quantization.