  We present an analytic two-loop calculation within the scalar diquark model
of the potential linear and angular momenta, defined as the difference between
the Jaffe-Manohar and Ji notions of linear and angular momenta. As expected by
parity and time-reversal symmetries, a direct calculation confirms that the
potential transverse momentum coincides with the Jaffe-Manohar (or canonical)
definition of average quark transverse momentum, also known as the quark Sivers
shift. We examine whether initial/final-state interactions at the origin of the
Sivers asymmetry can also generate a potential angular momentum in the scalar
diquark model.
