Radiatively generated parton distributions of real and virtual photons - art. no. 054019

The parton content of real (P-2=0) and virtual (P(2)not equal 0) transverse photons gamma(P-2) is expressed in terms of perturbative pointlike and non perturbative hadronic (VMD) components, employing recently updated parton d istributions of pions and protons. The resulting parameter-free and perturb atively stable LO and NLO parton densities f(gamma(P2))(x,Q(2)), smooth in P-2 and apply to all P(2)greater than or equal to 0 whenever gamma(P-2) is probed at scales Q(2) much greater than P-2 where transverse photons also d ominate physically relevant cross sections. Predictions are given for the s tructure function F-2(gamma(P2))(x,Q(2)) and f(gamma(P2))(x,Q(2)), and are compared with all relevant data for real photons as well as with recent dat a for virtual photons as extracted from DIS ep dijet events. Simple analyti c parametrizations of our predicted parton distributions are presented for the real photon in LO and NLO, and for the virtual photon in LO which, with in sufficient accuracy, may be also used in NLO-QCD. [S0556-2821(99)05915-9 ].