Spin structure functions and intrinsic motion of the constituents

Abstract

The spin structure functions of the system of quasifree fermions on mass shell are studied in a consistently covariant approach. Comparison with the basic formulas following from the quark-parton model reveals the importance of the fermion motion inside the target for the correct evaluation of the spin structure functions. In particular it is shown, that regarding the moment ${\Gamma }_1$, both the approaches are equivalent for the static fermions, but differ by the factor 1/3 in the limit of massles fermions (, in target rest frame). Some other sum rules are discussed as well.

Comments: 12 pages, Tex. In this slightly modified version one more sum rule is added. The paper is accepted for publication in Phys. Rev. D