V.D334 — 21cm Brightness Temperature

Differential brightness temperature T₂₁(z) ≈ 27 mK · x_HI · (1−T_CMB/T_S) · √((1+z)/10 · 0.15/Ω_m) · (ω_b/0.023). Uses exclusively τ-native inputs: Ω_m=0.315, ω_b=0.02238. Zero free parameters.