520 research outputs found
Wide angle Compton scattering on the proton: study of power suppressed corrections
We study the wide angle Compton scattering process on a proton within the
soft collinear factorization (SCET) framework. The main purpose of this work is
to estimate the effect due to certain power suppressed corrections. We consider
all possible kinematical power corrections and also include the subleading
amplitudes describing the scattering with nucleon helicity flip. Under certain
assumptions we present a leading-order factorization formula for these
amplitudes which includes the hard- and soft-spectator contributions. We apply
the formalism and perform a phenomenological analysis of the cross section and
asymmetries in the wide angle Compton scattering on a proton. We assume that in
the relevant kinematical region where ~GeV the dominant
contribution is provided by the soft-spectator mechanism. The hard coefficient
functions of the corresponding SCET operators are taken in the leading-order
approximation. The analysis of existing cross section data shows that the
contribution of the helicity flip amplitudes to this observable is quite small
and comparable with other expected theoretical uncertainties. We also show
predictions for double polarization observables for which experimental
information exists.Comment: 15 pages, 5 figure
One Loop Chiral Corrections to Hard Exclusive Processes:I. Pion Case
We computed the leading non-analytic chiral corrections to the generalized
parton distributions (GPDs) of the pion and to the two-pion distribution
amplitudes. This allows us to obtain the corresponding corrections for the hard
exclusive processes, such as gamma^* gamma -> pi pi, gamma^* N -> 2pi N' and
deeply virtual Compton scattering on the pion target.Comment: 17 pages, 3 figure
Electroproduction of tensor mesons in QCD
Due to multiple possible polarizations hard exclusive production of tensor
mesons by virtual photons or in heavy meson decays offers interesting
possibilities to study the helicity structure of the underlying short-distance
process. Motivated by the first measurement of the transition form factor
at large momentum transfers by the BELLE
collaboration we present an improved QCD analysis of this reaction in the
framework of collinear factorization including contributions of twist-three
quark-antiquark-gluon operators and an estimate of soft end-point corrections
using light-cone sum rules. The results appear to be in a very good agreement
with the data, in particular the predicted scaling behavior is reproduced in
all cases.Comment: 27 pages, 5 figure
On chiral corrections to nucleon GPD
Within the pion-nucleon chiral perturbation theory we derive the leading
chiral correction to the nucleon GPD at . We discuss the difficulties of
consideration of nonlocal light-cone operators within the theory with a heavy
particle and the methods to solve the difficulties. The consideration of the
chiral corrections directly for nonlocal operators allows to resolve the
ambiguity of the inverse Mellin transformation. In particular, we show that the
mixing between axial and vector GPDs are of order , which is two
orders of magnitude less that it follows from the Mellin moments calculation.Comment: 17 pages, 1 figure; minor corrections in the tex
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