Anatomy of the differential gluon structure function of the proton from the experimental data on F-2p(x,Q(2))

The differential gluon structure function of the proton F(x,Q(2)) introduced by Fadin, Kuraev, and Lipatov in 1975 is used in many applications of small-x QCD. We report here ready-to-use parametrizations of F(x,Q(2)) from the kappa-factorization phenomenology of the experimental data on the small-x proton structure function F-2p(x,Q(2)). These parametrizations are based partly on the available Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution fits [Gluck-Reya-Vogt, Coordinated Theoretical/Experimental project on QCD Phenomenology (CTEQ), and Martin-Roberts-Stirling] to parton distribution functions and on realistic extrapolations into a soft region. We discuss the impact of soft gluons on various observables. The x dependence of the F(x,Q(2)) so determined varies strongly with Q(2) and does not exhibit simple Regge properties. Nonetheless, the hard-to-soft diffusion is found to give rise to a viable approximation of the proton Structure function F-2p(x,Q(2)) by the soft and hard Regge components with intercepts Delta(soft)=0 and Delta(hard)similar to0.4.