The MOND Acceleration Scale from Rindler-de Sitter Thermodynamics

We derive the MOND acceleration scale from Rindler–de Sitter thermodynamics. If the Rindler horizon distance of a uniformly accelerated observer equals the Gibbons–Hawking thermal de Broglie wavelength λT_H = 2πc/H, then a_0 = cH/2π. The factor 2π arises directly from the KMS period of the Euclidean de Sitter propagator and is not fitted. The Deser–Levin quadratic temperature addition law then supplies the interpolating function μ(x) = x/√(1 + x²). These two inputs uniquely determine a ghost-free covariant AQUAL action F(Q) = √(Q + Q²) − arcsinh(√Q) that satisfies the null and weak energy conditions, reduces to Newtonian gravity at high acceleration, yields the exact BTFR exponent 4 in the deep-MOND limit, and enforces constant a_0 as a structural consequence of vacuum selection on R_vac = 4Λ (not an extra assumption). The predicted value cHdS/2π ≈ 0.94 × 10⁻¹⁰ m s⁻² (using the asymptotic de Sitter Hubble rate) lies 22 % below the SPARC best-fit of 1.20 × 10⁻¹⁰ m s⁻²; the residual is comparable to the present-day departure from exact de Sitter expansion. Gravitational-wave speed remains exactly c. Gravitational lensing requires a disformal metric completion and is deferred to future work. The central matching condition d_R = λT_H is a physically motivated postulate; a first-principles derivation (possibly from the holographic mode spectrum of the de Sitter boundary) remains the principal open problem of the framework.