On transverse spin sum rules

In this work we show that (i) both the form factors AiAi and C¯i contribute to the matrix element of the energy–momentum tensor Ti+− in a transversely polarized state, (ii) there is no relative suppression factor between these two contributions and (iii) the contribution to the matrix element of the Pauli–Lubanski operator Wi⊥ from that of Ti++ contains only the form factor BiBi and not the form factor AiAi. These results support our criticism and the conclusions as stated in Ref. [13]. Comparing and contrasting the spin sum rules in two different approaches, one advocated by us and the one proposed by Jaffe and Manohar, we point out that the physical content of the sum rules is very transparent in our approach, whereas, in the second approach details of the dynamics remain hidden and the separation into orbital and intrinsic spin parts is not visible.