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A. V. Belitsky

Publications and source records attributed to A. V. Belitsky.

At least 109 records · Page 6Linked to original sources
arXiv2001

Hard exclusive meson production at next-to-leading order

We evaluate perturbative next-to-leading order corrections to the hard exclusive leptoproduction of pi+ mesons on a transversely polarized proton target. A model dependent study shows that these corrections can be large. We analyze the scale dependence and explore the Brodsky-Lepage-Mackenzie scale setting procedure. Although the predictions for the cross section suffer from theoretical uncertainties, the transverse nucleon single spin asymmetry turns out to be a rather stable observable since higher order effects approximately cancel there.

hep-ph↗
arXiv2001

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.

hep-ph↗
arXiv2001

Twist-three analysis of photon electroproduction with pion

We study twist-three effects in spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering on a spin-zero target. Contributions which are power suppressed in 1/Q generate a new azimuthal angle dependence of the cross section which is not present in the leading twist results. On the other hand the leading twist terms are not modified by the twist three contributions. They may get corrected at twist four level. In the Wandzura-Wilczek approximation these new terms in the Fourier expansion with respect to the azimuthal angle are entirely determined by the twist-two skewed parton distributions. We also discuss more general issues like the general form of the angular dependence of the differential cross section, validity of factorization at twist-three level, and a relation of skewed parton distributions to spectral functions.

hep-ph↗
arXiv2001

Resummation of target mass corrections in two-photon processes: twist-two sector

We develop a formalism for the resummation of target mass corrections in off-forward two-photon amplitudes given by a chronological product of electromagnetic currents, arising in e.g. deeply virtual Compton scattering. The method is based on a relation of composite operators with a definite twist to harmonic tensors, which form an irreducible representation of the Lorentz group. We give an application of the framework for the matrix elements of twist-two operators.

hep-ph↗
arXiv2000

The Singlet g_2 Structure Function in the Next-to-Leading Order

Following a previous study of the one-loop factorization of the nonsinglet $g_2$ structure function of the nucleon, we present in this paper the next-to-leading order coefficient functions in the singlet sector. To obtain the result, the partonic processes of virtual Compton scattering off two and three "on-shell" gluons are calculated. A key step in achieving the correct factorization is to separate the correct twist-two contribution. The Burkardt-Cottingham sum rule is nominally satisfied at this order.

hep-ph↗
arXiv2000

Superconformal constraints for QCD conformal anomalies

Anomalous superconformal Ward identities and commutator algebra in N = 1 super-Yang-Mills theory give rise to constraints between the QCD special conformal anomalies of conformal composite operators. We evaluate the superconformal anomalies that appear in the product of renormalized conformal operators and the trace anomaly in the supersymmetric spinor current and check the constraints at one-loop order. In this way we prove the universality of QCD conformal anomalies, which define the non-diagonal part of the anomalous dimension matrix responsible for scaling violations of exclusive QCD amplitudes at the next-to-leading order.

hep-ph↗
arXiv2000

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.

hep-ph↗
arXiv2000

Twist-three effects in two-photon processes

We give a general treatment of twist-three effects in two-photon reactions. We address the issue of the gauge invariance of the Compton amplitude in generalized Bjorken kinematics and relations of twist-three `transverse' skewed parton distributions to twist-two ones and interaction dependent three-particle correlation functions. Finally, we discuss leading order evolution of twist-three functions and their impact on the deeply virtual Compton scattering.

hep-ph↗
arXiv2000

Integrability of twist-three evolution equations in QCD

We describe a recent progress in finding solutions to three-particle evolution equations at leading order in the QCD coupling constant for multiparton correlation functions based on the integrability of corresponding interaction Hamiltonians.

hep-ph↗
arXiv2000

NLO Exclusive Evolution Kernels

We outline a formalism used for a construction of two-loop flavor singlet exclusive evolution kernels in the MS bar scheme. The approach is based on the known pattern of conformal symmetry breaking in MS bar as well as constraints arising from the superconformal algebra of the N = 1 super Yang-Mills theory.

hep-ph↗
arXiv2000

Yang-Mills- and D-instantons

In these lectures, which are written at an elementary and pedagogical level, we discuss general aspects of (single) instantons in SU(N_c) Yang-Mills theory, and then specialize to the case of N = 4 supersymmetry and the large N_c limit. We show how to determine the measure of collective coordinates and compute instanton corrections to certain correlation functions. We then relate this to D-instantons in type IIB supergravity. By taking the D-instantons to live in an $AdS_5\times S^5$ background, we perform explicit checks of the AdS/CFT correspondence.

hep-th↗
arXiv2000

Off-forward gluonometry

We explore the deeply virtual Compton scattering process at NLO with the emphasis on the measurement of the tensor gluon skewed distributions. We recalculate the one-loop coefficient function and give two-loop results for anomalous dimensions and exclusive evolution kernels required for studying the logarithmic scaling violation. We evaluate weighted cross sections which give direct access to these functions on experiment.

hep-ph↗
arXiv2000

Instantons, Euclidean supersymmetry and Wick rotations

We discuss the reality properties of the fermionic collective coordinates in Euclidean space in an instanton background and construct hermitean actions for N = 4 and N = 2 supersymmetric Euclidean Yang-Mills theories.

hep-th↗
arXiv1999

Evolution kernels of skewed parton distributions: method and two-loop results

We present a formalism and explicit results for two-loop flavor singlet evolution kernels of skewed parton distributions in the minimal subtraction scheme. This approach avoids explicit multiloop calculations in QCD and is based on the known pattern of conformal symmetry breaking in this scheme as well as constraints arising from the graded algebra of the $\cN = 1$ super Yang-Mills theory. The conformal symmetry breaking part of the kernels is deduced from commutator relations between scale and special conformal anomalies while the symmetric piece is recovered from the next-to-leading order splitting functions and $\cN = 1$ supersymmetry relations.

hep-ph↗
arXiv1999

Radiative corrections to deeply virtual Compton scattering

We discuss possibilities of measurement of deeply virtual Compton scattering amplitudes via different asymmetries in order to access the underlying skewed parton distributions. Perturbative one-loop coefficient functions and two-loop evolution kernels, calculated recently by a tentative use of residual conformal symmetry of QCD, are used for a model dependent numerical estimation of scattering amplitudes.

hep-ph↗
arXiv1999

Renormalization of twist-three operators and integrable lattice models

We address the problem of solution of the QCD three-particle evolution equations which govern the Q-dependence of the chiral-even quark-gluon-quark and three-gluon correlators contributing to a number of asymmetries at leading order and the transversely polarized structure function g_2(x). The quark-gluon-quark case is completely integrable in multicolour limit and corresponds to a spin chain with non-periodic boundary conditions, while the pure gluonic sector contains, apart from a piece in the Hamiltonian equivalent to XXX Heisenberg magnet of spin s = - 3/2, a non-integrable addendum which can be treated perturbatively for a bulk of the spectrum except for a few lowest energy levels. We construct a quasiclassical expansion with respect to the total conformal spin of the system and describe fairly well the energy spectra of quark-gluon-quark and three-gluon systems.

hep-ph↗
arXiv1999

Deeply virtual Compton scattering in next-to-leading order

We study the amplitude of deeply virtual Compton scattering in next-to-leading order of perturbation theory including the two-loop evolution effects for different sets of skewed parton distributions (SPDs). It turns out that in the minimal subtraction scheme the relative radiative corrections are of order 20-50%. We analyze the dependence of our predictions on the choice of SPD, that will allow to discriminate between possible models of SPDs from future high precision experimental data, and discuss shortly theoretical uncertainties induced by the radiative corrections.

hep-ph↗