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A. N. Manashov

Publications and source records attributed to A. N. Manashov.

At least 55 records · Page 3Linked to original sources
arXiv2013

Operator product expansion in QCD in off-forward kinematics: Separation of kinematic and dynamical contributions

We develop a general approach to the calculation of target mass and finite t=(p'-p)^2 corrections in hard processes which can be studied in the framework of the operator product expansion and involve momentum transfer from the initial to the final hadron state. Such corrections, which are usually referred to as kinematic, can be defined as contributions of operators of all twists that can be reduced to total derivatives of the leading twist operators. As the principal result, we provide a set of projection operators that pick up the "kinematic" part of an arbitrary flavor-nonsinglet twist-four operator in QCD. A complete expression is derived for the time-ordered product of two electromagnetic currents that includes all kinematic corrections to twist-four accuracy. The results are immediately applicable to the studies of deeply-virtual Compton scattering, transition gamma^*-> M gamma form factors and related processes. As a byproduct of this study, we find a series of "genuine" twist-four flavor-nonsinglet quark-antiquark-gluon operators which have the same anomalous dimensions as the leading twist quark-antiquark operators.

hep-ph↗
arXiv2012

Scale dependence of twist-three contributions to single spin asymmetries

We reexamine the scale dependence of twist-three correlation functions relevant for the single transverse spin asymmetry in the framework of collinear factorization. Evolution equations are derived for both the flavor-nonsinglet and flavor--singlet distributions and arbitrary parton momenta. Our results do not agree with the recent calculations of the evolution in the limit of vanishing gluon momentum. Possible sources for this discrepancy are identified.

hep-ph↗
arXiv2012

Finite-t and target mass corrections to deeply virtual Compton scattering

We carry out the first complete calculation of kinematic power corrections ~t/Q^2 and ~m^2/Q^2 to the helicity amplitudes of deeply virtual Compton scattering. This result removes an important source of uncertainties in the QCD predictions for intermediate momentum transfers Q^2 ~ 1-10 GeV^2 that are accessible in the existing and planned experiments. In particular the finite-t corrections are significant and must be taken into account in the data analysis.

hep-ph↗
arXiv2012

Finite-t and target mass corrections to DVCS on a scalar target

Using the formalism developed in [1,2] we carry out the first complete calculation of kinematic power corrections to the helicity amplitudes of deeply-virtual Compton scattering to the twist-four accuracy for a study case of a (pseudo)scalar target. Our main result is that both finite-t, ~t/Q^2, and target mass, ~m^2/Q^2, twist-four kinematic power corrections turn out to be factorizable, at least to the leading order in the strong coupling. The structure of these corrections is discussed and a short model study of their numerical impact is presented.

hep-ph↗
arXiv2011

Finite-t and target mass corrections in off-forward hard reactions

We describe a systematic approach [1] to the calculation of kinematic corrections ~ t/Q^2, m^2/Q^2 in hard exclusive processes which involve momentum transfer from the initial to the final hadron state. As an example, the complete expression is derived for the time-ordered product of two electromagnetic currents that includes all kinematic corrections due to the quark distribution to twist-four accuracy. The results are applicable e.g. to the studies of deeply-virtual Compton scattering.

hep-ph↗
arXiv2011

Two-loop renormalization of three-quark operators in QCD

Renormalization of composite three-quark operators in dimensional regularization is complicated by the mixing of physical and unphysical (evanescent) operators. This mixing must be taken into account in a consistent subtraction scheme. In this work we propose a particular scheme that allows one to avoid the necessity of additional finite renormalization and is convenient in QCD applications. As an illustration, we calculate the two-loop anomalous dimensions of local three-quark operators in this scheme.

hep-ph↗
arXiv2011

Kinematic power corrections in off-forward hard reactions

We develop a general approach to the calculation of kinematic corrections ~t/Q^2, ~m^2/Q^2 in hard processes which involve momentum transfer from the initial to the final hadron state. As the principal result, the complete expression is derived for the time-ordered product of two electromagnetic currents that includes all kinematic corrections to twist-four accuracy. The results are immediately applicable e.g. to the studies of deeply-virtual Compton scattering.

hep-ph↗
arXiv2011

Twist-four Corrections to Parity-Violating Electron-Deuteron Scattering

Parity violating electron-deuteron scattering can potentially provide a clean access to electroweak couplings that are sensitive to physics beyond the Standard Model. However hadronic effects can contaminate their extraction from high-precision measurements. Power-suppressed contributions are one of the main sources of uncertainties along with charge-symmetry violating effects in leading-twist parton densities. In this work we calculate the twist-four correlation functions contributing to the left-right polarization asymmetry making use of nucleon multiparton light-cone wave functions.

hep-ph↗
arXiv2011

Higher twist parton distributions from light-cone wave functions

We explore the possibility to construct higher-twist parton distributions in a nucleon at some low reference scale from convolution integrals of the light-cone wave functions (WFs). To this end we introduce simple models for the four-particle nucleon WFs involving three valence quarks and a gluon with total orbital momentum zero, and estimate their normalization (WF at the origin) using QCD sum rules. We demonstrate that these WFs provide one with a reasonable description of both polarized and unpolarized gluon parton densities at large values of Bjorken variable x > 0.5. Twist-three parton distributions are then constructed as convolution integrals of qqqg and usual three-quark WFs. The cases of the polarized structure function g_2(x,Q^2) and single transverse spin asymmetries are considered in detail. We find that the so-called gluon-pole contribution to twist-three distributions relevant for single spin asymmetry vanishes in this model, but is generated perturbatively at higher scales by the evolution, in the spirit of GRV parton distributions.

hep-ph↗
arXiv2011

Noncompact sl(N) spin chains: BGG-resolution, Q-operators and alternating sum representation for finite dimensional transfer matrices

We study properties of transfer matrices in the sl(N) spin chain models. The transfer matrices with an infinite dimensional auxiliary space are factorized into the product of N commuting Baxter Q-operators. We consider the transfer matrices with auxiliary spaces of a special type (including the finite dimensional ones). It is shown that they can be represented as the alternating sum over the transfer matrices with infinite dimensional auxiliary spaces. We show that certain combinations of the Baxter Q-operators can be identified with the Q-functions which appear in the Nested Bethe Ansatz.

nlin.SI↗
arXiv2009

Renormalization of Twist-Four Operators in QCD

Extending the work by Bukhvostov, Frolov, Lipatov and Kuraev (BFLK) on the renormalization of quasipartonic operators we derive a complete set of two-particle renormalization group kernels that enter QCD evolution equations to twist-four accuracy. It is shown that the 2->2 evolution kernels which involve ``non-partonic'' components of field operators, and, most remarkably, also 2->3 kernels do not require independent calculation and can be restored from the known results for quasipartonic operators using conformal symmetry and Lorentz transformations. The kernels are presented for the renormalization of light-ray operators built of chiral fields in a particular basis such that the conformal symmetry is manifest. The results can easily be recast in momentum space, in the form of evolution equations for generalized parton distributions.

hep-ph↗
arXiv2009

Baryon Operators of Higher Twist in QCD and Nucleon Distribution Amplitudes

We develop a general theoretical framework for the description of higher-twist baryon operators which makes maximal use of the conformal symmetry of the QCD Lagrangian. The conformal operator basis is constructed for all twists. The complete analysis of the one-loop renormalization of twist-4 operators is given. The evolution equation for three-quark operators of the same chirality turns out to be completely integrable. The spectrum of anomalous dimensions coincides in this case with the energy spectrum of the twist-4 subsector of the SU(2,2) Heisenberg spin chain. The results are applied to give a general classification and calculate the scale dependence of subleading twist-4 nucleon distribution amplitudes that are relevant for hard exclusive reactions involving a helicity flip. In particular we find an all-order expression (in conformal spin) for the contributions of geometric twist-3 operators to the (light-cone) twist-4 nucleon distribution amplitudes, which are usually referred to as Wandzura-Wilczek terms.

hep-ph↗
arXiv2009

Factorization of R-matrix and Baxter Q-operators for generic sl(N) spin chains

We develop an approach for constructing the Baxter Q-operators for generic sl(N) spin chains. The key element of our approach is the possibility to represent a solution of the the Yang Baxter equation in the factorized form. We prove that such a representation holds for a generic sl(N) invariant R-operator and find the explicit expression for the factorizing operators. Taking trace of monodromy matrices constructed of the factorizing operators one defines a family of commuting (Baxter) operators on the quantum space of the model. We show that a generic transfer matrix factorizes into the product of N Baxter Q-operators and discuss an application of this representation for a derivation of functional relations for transfer matrices.

nlin.SI↗
arXiv2006

Baxter Q-operator for graded SL(2|1) spin chain

We study an integrable noncompact superspin chain model that emerged in recent studies of the dilatation operator in the N=1 super-Yang-Mills theory. It was found that the latter can be mapped into a homogeneous Heisenberg magnet with the quantum space in all sites corresponding to infinite-dimensional representations of the SL(2|1) group. We extend the method of the Baxter Q-operator to spin chains with supergroup symmetry and apply it to determine the eigenspectrum of the model. Our analysis relies on a factorization property of the R-operators acting on the tensor product of two generic infinite-dimensional SL(2|1) representations. It allows us to factorize an arbitrary transfer matrix into a product of three `elementary' transfer matrices which we identify as Baxter Q-operators. We establish functional relations between transfer matrices and use them to derive the TQ-relations for the Q-operators. The proposed construction can be generalized to integrable models based on supergroups of higher rank and, in distinction to the Bethe Ansatz, it is not sensitive to the existence of the pseudovacuum state in the quantum space of the model.

hep-th↗
arXiv2006

Baxter operators for the quantum sl(3) invariant spin chain

The noncompact homogeneous sl(3) invariant spin chains are considered. We show that the transfer matrix with generic auxiliary space is factorized into the product of three sl(3) invariant commuting operators. These operators satisfy the finite difference equations in the spectral parameters which follow from the structure of the reducible sl(3) modules.

nlin.SI↗
arXiv2005

Superconformal operators in Yang-Mills theories on the light-cone

We employ the light-cone superspace formalism to develop an efficient approach to constructing superconformal operators of twist two in Yang-Mills theories with N=1,2,4 supercharges. These operators have an autonomous scale dependence to one-loop order and determine the eigenfunctions of the dilatation operator in the underlying gauge theory. We demonstrate that for arbitrary N the superconformal operators are given by remarkably simple, universal expressions involving the light-cone superfields. When written in components field, they coincide with the known results obtained by conventional techniques.

hep-th↗
arXiv2004

Quantum integrability in (super) Yang-Mills theory on the light-cone

We employ the light-cone formalism to construct in the (super) Yang-Mills theories in the multi-color limit the one-loop dilatation operator acting on single trace products of chiral superfields separated by light-like distances. In the N=4 Yang-Mills theory it exhausts all Wilson operators of the maximal Lorentz spin while in nonsupersymmetric Yang-Mills theory it is restricted to the sector of maximal helicity gluonic operators. We show that the dilatation operator in all N-extended super Yang-Mills theories is given by the same integral operator which acts on the (N+1)-dimensional superspace and is invariant under the SL(2|N) superconformal transformations. We construct the R-matrix on this space and identify the dilatation operator as the Hamiltonian of the Heisenberg SL(2|N) spin chain.

hep-th↗