Canonical and kinetic decompositions of the proton spin

Abstract

We propose a short summary of the present situation concerning the proton spin decomposition. We briefly discuss some of the main controversies about the issues of gauge invariance, uniqueness and measurability. As a conclusion, we argue that part of the controversies is actually undecidable.

Comments: 4 pages, contribution to the proceedings of the 3rd Workshop on the QCD Structure of the Nucleon (QCD-N'12), Oct 22-26, Bilbao, Spain