An estimate of higher twist at small [equation] and low [equation] based upon a Saturation Model

摘要

We investigate the influence of higher twist corrections to deep inelastic structure functions in the low-(Q^2) 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 (F_2). 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 (F_L) or (F_T) but in (F_2=F_L + F_T) they almost cancel. This indicates the limitation on the use of the DGLAP formalism at small x and (Q^2). We point out that (F_L) analysis needs a large twist-4 correction. We also indicate the region of validity of the twist expansion.