Froissart boundary for deep inelastic structure functions
  In this letter we derive the Froissart boundary in QCD for the deep inelastic structure function in low $x$ kinematic region. We show that the comparison of the Froissart boundary with the new HERA experimental data gives rise to a challenge for QCD to explain the matching between the deep inelastic scattering and real photoproduction process. 
A.L.Ayala (IF UFRGS), M.B.Gay Ducati (IF UFRGS), E.M.Levin (ANL/PNPI)