UNITARITY BOUNDARY FOR DEEP-INELASTIC STRUCTURE FUNCTIONS

In this letter we derive the unitarity boundaries in QCD for the deep inelastic structure function in low x kinematic region: the Froissart boundary and a more restricted one, linked with experiment and based o n additional assumptions, justified in the leading log approximation o f perturbative QCD. The comparison of the unitarity boundaries with th e new HERA experimental data gives rise to a challenge for QCD to expl ain the matching between the deep inelastic scattering and real photop roduction process.