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arXiv · hep-ph/0103137

Spin-Dependent Structure Functions of Real and Virtual Photons

M. Gluck·E. Reya·C. Sieg
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Abstract

The implications of the positivity constraint, $|g_1^{γ(P^2)}(x,Q^2)| \leq F_1^{γ(P^2)}(x,Q^2)$, on the presently unknown spin--dependent structure function $g_1^{γ(P^2)}(x,Q^2)$ of real and virtual photons are studied at scales $Q^2\gg P^2$ where longitudinally polarized photons dominate physically relevant cross sections. In particular it is shown how to implement the physical constraints of positivity and continuity at $P^2=0$ in NLO calculations which afford a nontrivial choice of suitable (DIS) factorization schemes related to $g_1^γ$ and $F_1^γ$ and appropriate boundary conditions for the polarized parton distributions of real and virtual photons. The predictions of two extreme `maximal' and `minimal' saturation scenarios are presented and compared with results obtained within the framework of a simple quark `box' calculation expected to yield reasonable estimates in the not too small regions of $x$ and $P^2$.

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M. Gluck, E. Reya, C. Sieg. 2001-03-13. Spin-Dependent Structure Functions of Real and Virtual Photons. https://doi.org/10.1007/s100520100677

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