1 II. Institut für Theoretische Physik,
Universität Hamburg, Luruper Chaussee 149,
2 Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Krakow, Poland
Received: 20 March 2000 / Published online: 9 August 2000 - © Springer-Verlag 2000
We investigate the influence of higher twist corrections to deep inelastic structure functions in the low-Q2 and small-x HERA region. We review the general features of the lowest-order QCD diagrams which contribute to twist-4 at small-x, in particular the sign structure of longitudinal and transverse structure functions which offers the possibility of strong cancellations in F2. For a numerical analysis we perform a twist analysis of the saturation model which has been very successful both in describing the structure function and the DIS diffractive cross section at HERA. As the main conclusion, twist 4 corrections are not small in FL or FT but in F2=FL + FT they almost cancel. This indicates the limitation on the use of the DGLAP formalism at small x and Q2. We point out that FL analysis needs a large twist-4 correction. We also indicate the region of validity of the twist expansion.
Copyright Società Italiana di Fisica, Springer-Verlag 2000