Instantons and saturation in the colour dipole picture

We pursue the intriguing possibility that larger-size instantons build up diffractive scattering, with the marked instanton-size scale left angle ρ right angle ∼ 0.5 fm being reflected in the conspicuous ''geometrization'' of soft QCD. As an explicit illustration, the known instanton contribution to DIS is transformed into the intuitive colour dipole picture. With the help of lattice results, the qq-dipole size r is carefully increased towards hadronic dimensions. Unlike pQCD, one now observes a competition between two crucial length scales: the dipole size r and the size ρ of the background instanton that is sharply localized around left angle ρ right angle ∼ 0.5 fm. For r >or∼ left angle ρ right angle, the dipole cross section indeed saturates towards a geometrical limit, proportional to the area π left angle ρ right angle 2, subtended by the instanton. (orig.)