Tensor-structure sum rules for spin-1 targets at all $Q^2$

Abstract

We derive a family of sum rules for the tensor structure functions of targets with spin one or higher, rooted in exact Siegert relations. The mixed rank-two $TT$--$LT$ degeneracy combines amplitudes of opposite crossing parity and, under the superconvergence assumption, gives ${\int }_0^{1}dx[b_2(x,Q^2)-3b_4(x,Q^2)]=0$ in the Hoodbhoy--Jaffe--Manohar (HJM) basis. At large $Q^2$, the protected moment agrees with Detmold's target-mass-complete twist-two OPE; in the strict Bjorken projection, and if $b_4$ is neglected, it reduces to the Efremov--Teryaev (ET)-type condition ${\int }_0^{1}dxx{b}_1(x)=0$, whose measured-range footprint is consistent with the HERMES data. Two further rank-two combinations connect crossing-even amplitudes and determine the corresponding subtraction functions through weighted HJM moments. The protected combination can be isolated through separated tensor $LT$ and $TT$ responses, providing a direct experimental strategy for JLab and, ultimately, a future EIC.

Comments: 18 pages, 2 figures