Along with the development of Deep Inelastic Scattering experiments, there has been a growing interest to fully understand the nucleons structure. In particular, there is nowadays a great interest in the decomposition of its total angular momentum into orbital angular momentum (OAM) and intrinsic spin, as well as identifying contributions from valence quarks, sea quarks and gluons.
The most common decompositions of OAM are the Jaffe-Manohar (canonical) and Ji (kinetic) decompositions, which differ in the way contributions are attributed to either quarks or gluons. Using perturbation theory, explicit one-loop calculations have found that the difference between such decompositions vanishes in QED. We show within the scalar diquark model in QED that the discrepancy appears at two-loop level, supporting the interpretation of such inequality as originating from the torque exerted by the spectator system on the struck quark.