Higher Twist Contributions to Deep-Inelastic Structure Functions

In wide kinematic regions the deeply inelastic structure functions can be described by their leading twist contributions within Quantum Chromodynamics (QCD). Higher twist corrections [1] emerge both in the region of large [2,3] and small values [4,5] of the Bjorken variable x. The leading twist sector, both for unpolarized and polarized deeply inelastic scattering, is well explored within perturbative QCD up to the level of 3–loop, resp. 2–loop, corrections [6, 7], including the heavy flavor contributions [8]. On the other hand, very little is known on the scaling violations of dynamical next-to-leading twist correlation functions and the associated Wilson coefficients [1], even on the leading order level. In many experimental and phenomenological analyzes, cf. [2, 3], higher twist contributions are parameterized by an ‘Ansatz’ [2], which is fitted accordingly. Within QCD this ad-hoc treatment cannot be justified, performing at the same time a higher order analysis for the leading twist terms. Since neither the corresponding higher twist anomalous dimensions nor Wilson coefficients were calculated, the data analysis has to be limited in the first place to the kinematic domain in which higher twist terms can be safely disregarded. In the following we report on the determination of the higher twist contributions in the deeply-inelastic structure functions F ep,ed 2 (x,Q ), see Ref. [9] for details. Higher twist contributions were also studied in deep-inelastic neutrino scattering, cf. [10]. Also in the case of polarized deeply inelastic scattering higher twist corrections are present in general. Since the polarized structure functions are measured through an asymmetry, the effect of higher twist contributions in the denominator function has to be known in detail. In [11] no significant higher twist contributions were found. Other authors claim contributions in the low x region [12], which is also the region of very low values of Q. These effects need further study. In the case of the structure functions F ep,ed 2 (x,Q ) we investigate the flavor non-singlet contributions in the large x region for Q ≥ 4GeV,W 2 ≥ 12.5GeV, cf. [13]. a One generally may consider flavor non-singlet combinations and perform a three-loop QCD analysis, which requires the O(αs) Wilson coefficients [15] and the 3–loop anomalous dimensions [6].