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.