Nonperturbative effects in gluon radiation and photoproduction of quark pairs -: art. no. 054022

We introduce a nonperturbative interaction for light-cone fluctuations containing quarks and gluons, The (q) over bar q interaction squeezes the transverse size of these fluctuations in the photon and one does not need to simulate this effect via effective quark masses. The strength of this interaction is fixed by data. Data on diffractive dissociation of hadrons and photons show that the nonperturbative interaction of gluons is much stronger. We fix the parameters for the nonperturbative quark-gluon interaction by data fur:diffractive dissociation to large masses (triple-Pomeron regime). This allows us to predict nuclear shadowing for gluons which turns out to be not as strong as perturbative QCD predicts. We expect a delayed onset of gluon shadowing at x less than or equal to 10(-2) shadowing of quarks. Gluon shadowing turns out to be nearly scale invariant up to virtualities Q(2)similar to 4 GeV2 due to the presence of a semihard scale characterizing the strong nonperturbative interaction of gluons. We use the same concept to improve our description of gluon bremsstrahlung which is related to the distribution function for a quark-gluon fluctuation and the interaction cross section of a (q) over bar qG fluctuation with a nucleon. We expect the nonperturbative interaction to suppress dramatically the gluon radiation at small transverse momenta compared to perturbative calculations.