Galactic Rotation Curves from the de Sitter Horizon

The empirical MOND acceleration constant a0≈1.2×10−10 m/s² is numerically close to cH0/(2π) — the acceleration associated with the Gibbons–Hawking temperature of the de Sitter horizon. We define au=cH0/(2π) and test it against 171 SPARC galaxies with a holographic interpolation function, with au fixed globally and only stellar mass-to-light ratios free. The holographic model achieves median χ2/ν=1.45, outperforming MOND simple (1.53) and MOND standard (1.52) despite having zero global free parameters. A 2×2 isolation test separates the contributions: (i) au outperforms a0 within MOND's own interpolation function (102/171 galaxies, 59.6%); (ii) the holographic interpolation outperforms MOND simple within the same acceleration scale (113/171, 66.1%). Both effects are independent and robust across all error treatments. MOND simple with au substituted for a0 achieves the lowest median χ2/ν of any configuration (1.41). The prediction au(z)=cH(z)/(2π) provides a falsifiable distinction from both CDM and MOND.