Abstract
<title>Abstract</title> <p>Disk-galaxy rotation curves require more centripetal acceleration than baryonic gravity provides. This paper formulates the missing acceleration as an equivalent force from local angular-momentum conservation. For an S^1 rotational symmetry, fixing angular momentum mu introduces an amended potential mu^2/(2I), whose gradient is the centrifugal covector; for I=mr^2 this gives mOmega^2 r. Applying this reduction to a thin galactic disk, each annulus is a local angular-momentum balance sector, with unresolved coherent transport represented by a finite-capacity closure coordinate. The resulting branch is g_AM = a_L[1-exp{-(g_bar/g_L)^{2/5}}], with a_L=cH_0/pi and g_L=a_L/lambda_L, lambda_L=9.170x10^-2, fixed before scoring. The exponent 2/5 is a thin-disk hypothesis, not a fitted shape. On raw SPARC data (175 galaxies, 3391 points), the fixed branch gives Q1+Q2 scatter 0.1914 dex and rotation-supported scatter 0.1742 dex, improves over baryon-only gravity by 0.26-0.28 dex, matches a same-protocol RAR-like baseline, and collapses under baryonic permutation by factors 4.20-4.30. The claim is limited: this is a rotation-curve closure for the equivalent force from localized angular-momentum balance, not a new microscopic force and not a complete replacement for cosmological dark matter.</p>