Axial Torsion Bounds from the Hydrogen Hyperfine Interval and Its Measurement Precision

This paper examines what the precisely known hydrogen hyperfine interval implies for a spin coupling to a uniform axial background. The system considered is ground-state hydrogen and the 21-centimetre hyperfine transition at 1420.405751768 MHz, and the observable is hyperfine frequency precision translated into an energy and torsion limit. Evaluating the ordinary behaviour of the system and the spin-torsion contribution under explicit assumptions about polarisation and uniformity, and inverting the comparison at the stated laboratory precision, gives a quantitative bound rather than a qualitative assertion of smallness. The computed record is: nu_Hz = 1.420e+09; fractional_precision = 1.000e-12; energy_uncertainty_J = 9.412e-37; torsion_bound_per_m = 2.977e-11; splitting_eV = 5.874e-06. The torsion-related contribution is far below the level that would alter the ordinary behaviour of the system at current precision, and the value that would have produced a visible residual is stated so that future improvements can be assessed against it directly. No new measurement is reported. This study is simulated and computed from stated assumptions, not measured.