E. Stein

NLO corrections to deeply virtual Compton scattering

Abstract We have calculated the NLO corrections to the twist-2 part of the deeply-virtual Compton scattering amplitude. Our results for the transverse and antisymmetric parts agree with recent calculations by Ji and Osborne and by Belitsky and Muller. In addition we present NLO results for the longitudinal part of the amplitude.

QCD sum rule calculation of twist-3 contributions to polarized nucleon structure functions

Abstract Using the framework of QCD sum rules we predict the twist-3 contribution to the second moment of the polarized nucleon structure function g 2 ( x ). As the relevant local operator depends explicitly on the gluon field, we employ a recently studied interpolating nucleon current which contains three quark field and one gluon field operator. Despite the fact that our calculation is based on the analysis of a completely different correlation function, our estimates are consistent with those of Balitsky, Braun and Kolesnichenko who used a three-quark current.

QCD sum rule calculation of twist-4 corrections to Bjorken and Ellis-Jaffe sum rules

Abstract We calculate the twist-4 corrections to the integral of g 1 ( x , Q 2 ) in the framework of QCD sum rules using an interpolating nucleon field which contains explicitly a gluonic degree of freedom. This information can be used together with previous calculations of the twist-3 contribution to the second moment of g 2 ( x ) to estimate the higher-twist corrections to the Ellis-Jaffe and Bjorken sum rules. We get f (2) (proton) = −0.037 ±0.006 and f (2) (neutron) = −0.013 ± 0.006. Numerically ou results roughly agree with those obtained by Balitsky, Braun and Kolesnichenko based on a sum rule for a simpler current. Our calculations are far more stable as tested within the sum rule approach but are more sensitive to less well known condensates.

IR-renormalon contribution to the longitudinal structure function FL

Abstract The available data on F L suggest the existence of unexpected large higher twist contributions. We use the 1 N f expansion to analyze the renormalon contribution to the coefficient function of the longitudinal structure function F L p − n . The renormalon ambiguity is calculated for all moments of the structure function thus allowing to estimate the contribution of “genuine” twist-4 corrections as a function of Bjorken- x . The predictions turn out to be in surprisingly good agreement with the experimental data.

Phenomenology of IR-renormalons in inclusive processes

Measurements of QCD observables have reached such high precision that power corrections to the structure functions can often be extracted with a reasonable accuracy from the existing data. The situation on the theoretical side is much less clear. In the best understood case of deep inelastic scattering, the relevant contributions can be attributed in the framework of operator product expansion (OPE) to matrix elements of higher-twist operators [1], but their determination in QCD is ambiguous due to occurrence of power divergences [2]. From the phenomenological point of view, however, attempts to compute these matrix elements using e.g., QCD sum rules have provided results which seem to have at least the right order of magnitude [3] as compared with available experimental estimates.

IR-renormalon contribution to the polarized structure function g1

Abstract An estimation of the higher twist contribution to the polarized nonsinglet structure function g 1 is given. Its first moment is generally assumed to be small but this could be due to a cancellation of its contribution in different Bjorken- x ranges. We estimate the magnitude of g 1 tw4 as a function of x in the framework of the renormalon method. The calculated higher-twist-correcti to g 1 turn out to be in fact small for all x values. The correction to the determination of the nonsinglet matrix element d NS (2) from data for transversely nucleon polarization due to the calculated higher twist effects is of order 10%.

IR-renormalon contribution to the polarized structure function g1 [Phys. Lett. B 383 (1996) 463]

An estimation of the higher twist contribution to the polarized nonsinglet structure function

Diffractive charged meson pair production

g_1

OPE analysis of the nucleon scattering tensor: a review including weak interactions and finite mass effects

is given. Its first moment is generally assumed to be small but this could be due to a cancellation of its contribution in different Bjorken-

QED in Strong Coulomb Fields: Charged Vacuum, Atomic Clock, and Correlated, Narrow e+e−-Lines

x