Nonaccreting constant-torque disk ($\bar{\nu }\Sigma =B{r}^{-1/2},\mathcal{G}=3\pi \sqrt{G{M}_{\ast }}B$)

A steady Keplerian disk can transport angular momentum by viscous stress with zero mass flux. The radial drift vanishes, but the torque is constant and nonzero. An inner source and outer sink must supply its boundary angular-momentum exchange. This is distinct from a decretion flow, which transports mass outward.