GLUON DISTRIBUTIONS IN REAL AND VIRTUAL PHOTON AND THE PHOTON STRUCTURE-FUNCTION

Gluon distributions in real and virtual photons are calculated using e volution equations in the NLO approximation. The quark distributions i n the photon determined on the basis of the QCD sum rule approach in [ 1] are taken as an input. It is shown that gluon distribution in the p hoton can be reliably determined up to x = 0.03 divided by 0.05, much lower than the corresponding values in the case of quark distributions . Two variants of the calculations are considered: (1) it is assumed t hat there are no intrinsic gluons in the photon at some low normalizat ion point Q(2) = Q(0)(2) similar to 1GeV(2); (2)it is assumed that glu onic content of the photon at low Q(0)(2) is described by gluonic cont ent of vector mesons rho, omega, phi. The gluon distributions in these two variants appear to be different. This fact permits one to clarify the origin of nonperturbative gluonic content of the photon by compar ing the results with experiment. Structure functions F-2(x) for real a nd virtual photon are calculated and it is shown that in the region x greater than or equal to 0.2 where QCD approach is valid, there is a g ood agreement with experiment.