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 $$\int_0^1! d x\,[b_2(x,Q<sup>2)-3b_4(x,Q<sup>2)]=0$$ in the Hoodbhoy--Jaffe--Manohar (HJM) basis. At large $Q<sup>2$, 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 $\int_0^1! d x\,x\,b_1(x)=0$, 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.