889 research outputs found
Twist-4 photon helicity-flip amplitude in DVCS on a nucleon in the Wandzura-Wilczek approximation
We computed twist-4 part of the photon spin-flip amplitude in deeply virtual
Compton scattering on a nucleon in the Wandzura-Wilczek approximation. We found
a factorizable contribution, which arises from photon scattering on quarks with
non-zero angular momentum along the collision axis. As the genuine twist-2
amplitude arises at the NLO, for moderate virtualities of the hard photon, GeV, kinematical twist-4 correction can give numerically important
contribution to the photon helicity-flip amplitude.Comment: 17 pages, 2 figures, added qualitative estimate of the magnitude of
twist-4 correction which seems to be larg
On scale dependence of QCD string operators
We have obtained a general solution of evolution equations for QCD twist-2
string operators in form of expansion over complete set of orthogonal
eigenfunctions of evolution kernels in coordinate-space representation. In the
leading logarithmic approximation the eigenfunctions can be determined using
constraints imposed by conformal symmetry. Explicit formulae for the LO
scale-dependence of quark and gluon twist-2 string operators are given
Conformal string operators and evolution of skewed parton distributions
We have investigated skewed parton distributions in coordinate space. We
found that their evolution can be described in a simple manner in terms of
non-local, conformal operators introduced by Balitsky and Braun. The resulting
formula is given by a Neumann series expansion. Its structure resembles, for
all values of the asymmetry parameter, the well-known solution of the ERBL
equation in the momentum space. Performing Fourier transformation we have
reproduced known results for evolution of momentum-space distributions.Comment: 24 pages, 2 figure
- …