We introduce a nonperturbative interaction for light-cone fluctuations containing quarks and gluons. Theqq 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 for diffractive dissociation to large masses (triple-Pomeron coupling). 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 shadowing at x ≤ 10 −2 due to the fact that photon fluctuations (containing a gluon) are heavier than in the case of quark shadowing. 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 aqqG fluctuation with a nucleon. We expect the nonperturbative interaction to suppress dramatically the gluon radiation at small transverse momenta. Also the Landau-Pomeranchuk suppression for gluon radiation of a quark propagating through a nucleus turns out to be smaller than predicted by perturbative QCD.

The density of gluons produced in the central rapidity region of a heavy ion collision is poorly known. We investigate the influence of the effects of quantum coherence on the transverse momentum distribution of photons and gluons radiated by a quark propagating through nuclear matter. We describe the case that the radiation time substantially exceeds the nuclear radius (the relevant case for RHIC and LHC energies), which is different from what is known as Landau-PomeranchukMigdal effect corresponding to an infinite medium. We find suppression of the radiation spectrum at small transverse photon/gluon momentum k T , but enhancement for k T > 1 GeV. Any nuclear effects vanish for k T ≥ 10 GeV. Our results allow also to calculate the k T dependent nuclear effects in prompt photon, light and heavy (Drell-Yan) dilepton and hadron production.