2,185 research outputs found
Baxter equation beyond wrapping
The Baxter-like functional equation encoding the spectrum of anomalous
dimensions of Wilson operators in maximally supersymmetric Yang-Mills theory
available to date ceases to work just before the onset of wrapping corrections.
In this paper, we work out an improved finite-difference equation by
incorporating nonpolynomial effects in the transfer matrix entering as its
ingredient. This yields a self-consistent asymptotic finite-difference equation
valid at any order of perturbation theory. Its exact solutions for fixed spins
and twists at and beyond wrapping order give results coinciding with the ones
obtained from the asymptotic Bethe Ansatz. Correcting the asymptotic energy
eigenvalues by the Luescher term, we compute anomalous dimensions for a number
of short operators beyond wrapping order.Comment: 10 page
Scaling violations and off-forward parton distributions: leading order and beyond
We give an outline of a formalism for the solution of the evolution equations
for off-forward parton distributions in leading and next-to-leading orders
based on partial conformal wave expansion and orthogonal polynomials
reconstruction.Comment: 3 pages, LaTeX, 3 figures, Talk given at the 7th International
Workshop on Deep Inelastic Scattring and QCD, DESY-Zeuthen, April 19-23, 199
NLO evolution kernels for skewed transversity distributions
We present a calculation of the two-loop evolution kernels of the twist-two
transversally polarized quark and linearly polarized gluon skewed parton
distributions in the minimal subtraction scheme and discuss a solution of the
evolution equations suitable for numerical implementations.Comment: 14 pages LaTe
Long-range SL(2) Baxter equation in N=4 super-Yang-Mills theory
Relying on a few lowest order perturbative calculations of anomalous
dimensions of gauge invariant operators built from holomorphic scalar fields
and an arbitrary number of covariant derivatives in maximally supersymmetric
gauge theory, we propose an all-loop generalization of the Baxter equation
which determines their spectrum. The equation does not take into account
wrapping effects and is thus asymptotic in character. We develop an asymptotic
expansion of the deformed Baxter equation for large values of the conformal
spin and derive an integral equation for the cusp anomalous dimension.Comment: Latex, 11 page
Exclusive electroproduction of lepton pairs as a probe of nucleon structure
We suggest the measurement of exclusive electroproduction of lepton pairs as
a tool to study inter-parton correlations in the nucleon via generalized parton
distributions in the kinematical region where this process is light-cone
dominated. We demonstrate how the single beam-spin asymmetry allows to perform
such kind of analysis and give a number of predictions for several experimental
setups. We comment on other observables which allow for a clean separation of
different species of generalized parton distributions.Comment: 4 pages RevTeX4, 6 figures, typo fixe
Theory of deeply virtual Compton scattering on the nucleon
We compute the cross section for leptoproduction of the real photon off the
nucleon, which is sensitive to the deeply virtual Compton scattering amplitude
with power accuracy. Our considerations go beyond the leading twist and involve
the complete analysis in the twist-three approximation. We discuss consequences
of the target and lepton beam polarizations for accessing the generalized
parton distributions from experimental measurements of the azimuthal angular
dependence of the final state photon or nucleon. We introduce several sets of
asymmetries, defined as Fourier moments with respect to the azimuthal angle,
which allow for a clear separation of the twist-two and -three sectors. Relying
on a simple ansatz for the generalized parton distributions, we give
quantitative estimates for azimuthal and spin asymmetries, discuss the
uncertainties of these predictions brought in by radiative corrections, and
compare them with experimental data as well as other theoretical expectations.
Furthermore, we derive a general parametrization of the DVCS amplitudes in the
region of small Bjorken variable.Comment: 76 pages, LaTeX, 16 figures, 3 tables, minor correction
Twist-three observables in deeply virtual Compton scattering on the nucleon
We study twist-three effects in deeply virtual Compton scattering on an
unpolarized spin-1/2 target. A careful definition of observables as Fourier
moments w.r.t. the azimuthal angle allows for a clear separation of twist-two
and -three effects. Although the latter are power suppressed, they give leading
contributions to the twist-three asymmetries and do not affect the twist-two
observables.Comment: 10 pages, LaTe
\cN = 1 supersymmetric constraints for evolution kernels
We provide a complete set of supersymmetric constraints for the anomalous
dimensions of the conformal twist-two operators to all orders of perturbation
theory. Employing them we derive new relations between the exclusive evolution
kernels and apply them in QCD in order to get definite predictions at leading
order and beyond.Comment: LaTeX, npb.sty required, 4 pages, Talk given at the 7th International
Workshop on Deep Inelastic Scattring and QCD, DESY-Zeuthen, April 19-23, 199
Reconstruction of non-forward evolution kernels
We develop a framework for the reconstruction of the non-forward kernels
which govern the evolution of twist-two distribution amplitudes and off-forward
parton distributions beyond leading order. It is based on the knowledge of the
special conformal symmetry breaking part induced by the one-loop anomaly and
conformal terms generated by forward next-to-leading order splitting functions,
and thus avoids an explicit two-loop calculation. We demonstrate the formalism
by applying it to the chiral odd and flavour singlet parity odd sectors.Comment: 13 pages, LaTeX, typos fixe
Integrability and WKB solution of twist-three evolution equations
We identify an integrable one-dimensional inhomogeneous three-site open spin
chain which arises in the problem of diagonalization of twist-three quark-gluon
evolution equations in QCD in the chiral-odd sector. Making use of the
existence of a non-trivial `hidden' integral of motion the problem of
diagonalization of the evolution kernels is reduced to the study of a second
order finite-difference equation which is solved in WKB approximation for large
conformal spins of the three-particle system. The energies (alias anomalous
dimensions) of eigenstates with different scale dependence are found in
limiting cases and compared with numerical calculations.Comment: 26 pages, LaTeX, 4 figures; typos fixe
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