Abstract
We investigate the photon structure functions at small Bjorken variable x in the framework of the holographic QCD, assuming dominance of the Pomeron exchange. The quasi-real photon structure functions are expressed as convolution of the Brower–Polchinski–Strassler–Tan (BPST) Pomeron kernel and the known wave functions of the U(1) vector field in the five-dimensional AdS space, in which the involved parameters in the BPST kernel have been fixed in previous studies of the nucleon structure functions. The predicted photon structure functions, as confronted with data, provide a clean test of the BPST kernel. The agreement between theoretical predictions and data is demonstrated, which supports applications of holographic QCD to hadronic processes in the nonperturbative region. Our results are also consistent with those derived from the parton distribution functions of the photon proposed by Glück, Reya, and Schienbein, implying realization of the vector meson dominance in the present model setup.
Highlights
A photon is a fundamental particle, instead of a nonperturbative composite like hadrons
Summary andInFthLγ iosflethtteerqwuaesih-arveaelipnhveostotingaintedthteheresgtirounctoufresmfuanlcl tBiojnosrkFen2γ variable x in a holographic QCD model. They were calculated by convoluting the BPST Pomeron kernel with the wave functions of the U(1) vector field in the five-dimensional AdS space
The predicted dependencies of F2γ(x, Q2) on x and Q2 are in agreement with the OPAL data, implying the predictive power of the present model setup, and that the Pomeron exchange picture can describe general deep inelastic scattering (DIS) processes at small x reasonably
Summary
A photon is a fundamental particle, instead of a nonperturbative composite like hadrons. In this letter we will investigate the photon structure functions at small x, adopting the Pomeron exchange picture in the framework of the holographic QCD. The model dependence is reduced, and the predicted photon structure functions, as confronted with data, serve as a clean check of the validity of the BPST kernel. Our results are consistent with those obtained from the parton distribution functions (PDFs) of the photon proposed by Gluck, Reya, and Schienbein [34] Because they included the hadronic component in the photon PDFs, which dominates at small x, this consistency may imply realization of the vector meson dominance in the present setup. Our predictions for the photon structure functions at very low x can be tested at future linear colliders
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