arXiv subjects

Oleg V. Teryaev

Publications and source records attributed to Oleg V. Teryaev.

30 records · Page 2Linked to original sources

arXiv2014

On the Evolution of Sum Rules for T-Odd Distribution and Fragmentation Functions

We test stability against probabilistic evolution of sum rules for transverse-momentum-dependent distribution and fragmentation functions. We find that preservation of the Burkardt sum rule for Sivers distribution functions is similar to the conservation of longitudinal momentum related to spin-averaged parton distributions. At the same time, preservation of the Schaefer-Teryaev sum rule for Collins functions is similar to preservation of the Burkhardt-Cottingham sum rule for the spin-dependent g_2 structure function.

hep-ph↗

arXiv2014

Spin effects and compactification

We consider the dynamics of Dirac particles moving in the curved spaces with one coordinate subjected to compactification and thus interpolating smoothly between three- and two-dimensional spaces. We use the model of compactification, which allows us to perform the exact Foldy-Wouthuysen transformation of the Dirac equation and then to obtain the exact solutions of the equations of motion for momentum and spin in the classical limit. The spin precesses with the variable angular velocity, and a "flick" may appear in the remnant two-dimensional space once or twice during the period. We note an irreversibility in the particle dynamics because the particle can always penetrate from the lower-dimensional region to the higher-dimensional region, but not inversely.

gr-qc↗

arXiv2013

Spin in an arbitrary gravitational field

We study the quantum mechanics of a Dirac fermion on a curved spacetime manifold. The metric of the spacetime is completely arbitrary, allowing for the discussion of all possible inertial and gravitational field configurations. In this framework, we find the Hermitian Dirac Hamiltonian for an arbitrary classical external field (including the gravitational and electromagnetic ones). In order to discuss the physical content of the quantum-mechanical model, we further apply the Foldy-Wouthuysen transformation, and derive the quantum equations of motion for the spin and position operators. We analyse the semiclassical limit of these equations and compare the results with the dynamics of a classical particle with spin in the framework of the standard Mathisson-Papapetrou theory and in the classical canonical theory. The comparison of the quantum mechanical and classical equations of motion of a spinning particle in an arbitrary gravitational field shows their complete agreement.

gr-qc↗

arXiv2011

Axial anomaly and mixing: from real to highly virtual photons

The relation for transition form factors of eta and eta' mesons is obtained by combining the exact nonperturbative QCD sum rule, following from the dispersive representation of axial anomaly, and quark-hadron duality. It is valid at all virtual photon momenta and allows one to express the transition form factors entirely in terms of meson decay constants. This relation is in a good agreement with experimental data.

hep-ph↗

arXiv2010

Axial anomaly as a collective effect of meson spectrum

We study the transition form factors of the light mesons in the kinematics, where one photon is real and other is virtual. Using the dispersive approach to axial anomaly we show that the axial anomaly in this case reveals itself as a collective effect of meson spectrum. This allows us to get the relation between possible corrections to continuum and to lower states within QCD method which does not rely on factorization hypothesis. We show, relying on the recent data of BaBar Collaboration, that the relative correction to continuum is quite small, and small correction to continuum can dramatically change the pion form factor.

hep-ph↗

arXiv2010

Nucleon spin structure and pQCD frontier on the move

The interplay between higher orders of the perturbative QCD (pQCD) expansion and higher-twist contributions in the analysis of recent Jefferson Lab data on the lowest moment of the spin-dependent proton $Γ_1^{p} (Q^2)$ at $0.05<Q^2< 3 {\rm GeV}^2$ is studied. We demonstrate that the values of the higher-twist coefficients $μ^{p,n}_{2k} $ extracted from the data by using the singularity-free analytic perturbation theory provide a better convergence of the higher-twist series than with the standard perturbative QCD. From the high-precision proton data, we extract the value of the singlet axial charge $a_0(1 {\rm GeV}^2)=0.33\pm0.05$. We observe a slow $Q^2$ dependence of fitted values of the twist coefficient $μ_4$ and $a_0$ when going to lower energy scales, which can be explained by the renormalization group evolution of $μ_4(Q^2)$ and $a_0(Q^2)$. As the main result, a good quantitative description of all the Jefferson Lab data sets down to $Q \simeq 350 MeV is achieved.

hep-ph↗

arXiv2009

Axial Anomaly and Mixing Parameters of Pseudoscalar Mesons

In this work the analysis of mixing parameters of the system involving eta, eta' mesons and some third massive state G is carried out. We use the generalized mixing scheme with three angles. The framework of the dispersive approach to Abelian axial anomaly of isoscalar non-singlet current and the analysis of experimental data of charmonium radiative decays ratio allow us to get a number of quite strict constraints for the mixing parameters. The analysis shows that the equal values of axial current coupling constants f_8 and f_0 are preferable which may be considered as a manifestation of SU(3) and chiral symmetry.

hep-ph↗

arXiv2009

Spin dynamics in gravitational fields of rotating bodies and the equivalence principle

We discuss the quantum and classical dynamics of a particle with spin in the gravitational field of a rotating source. A relativistic equation describing the motion of classical spin in curved spacetimes is obtained. We demonstrate that the precession of the classical spin is in a perfect agreement with the motion of the quantum spin derived from the Foldy-Wouthuysen approach for the Dirac particle in a curved spacetime. We show that the precession effect depends crucially on the choice of a tetrad. The results obtained are compared to the earlier computations for different tetrad gauges.

gr-qc↗

arXiv2008

Spin observables and spin structure functions: inequalities and dynamics

Model-independent identities and inequalities relating the various spin observables of a reaction are reviewed in a unified formalism, together with their implications for dynamical models, their physical interpretation, and the quantum aspects of the information carried by spins, in particular entanglement. These constraints between observables can be obtained from the explicit expression of the observables in terms of a set of amplitudes, a non-trivial algebraic exercise which can be preceded by numerical simulation with randomly chosen amplitudes, from anticommutation relations, or from the requirement that any polarisation vector is less than unity. The most powerful tool is the positivity of the density matrices describing the reaction or its crossed channels, with a projection to single out correlations between two or three observables. For the exclusive reactions, the cases of the strangeness-exchange proton-antiproton scattering and the photoproduction of pseudoscalar mesons are treated in some detail: all triples of observables are constrained, and new results are presented for the allowed domains. The positivity constraints for total cross-sections and single-particle inclusive reactions are reviewed, with application to spin-dependent structure functions and parton distributions. The corresponding inequalities are shown to be preserved by the evolution equations of QCD.

hep-ph↗

arXiv2008

Bjorken Sum Rule and pQCD frontier on the move

The reasonableness of the use of perturbative QCD notions in the region close to the scale of hadronization, i.e., below $\lesssim 1 \GeV$ is under study. First, the interplay between higher orders of pQCD expansion and higher twist contributions in the analysis of recent Jefferson Lab (JLab) data on the Generalized Bjorken Sum Rule function $Γ_1^{p-n} (Q^2)$ at $0.1<Q^2< 3 {\rm GeV}^2$ is studied. It is shown that the inclusion of the higher-order pQCD corrections could be absorbed, with good numerical accuracy, by change of the normalization of the higher-twist terms. Second, to avoid the issue of unphysical singularity (Landau pole at $Q=Λ\sim 400 \MeV $), we deal with the ghost-free Analytic Perturbation Theory (APT) that recently proved to be an intriguing candidate for a quantitative description of light quarkonia spectra within the Bethe-Salpeter approach. The values of the twist coefficients $μ_{2k} $ extracted from the mentioned data by using the APT approach provide a better convergence of the higher-twist series than with the common pQCD. As the main result, a good quantitative description of the JLab data down to $Q\simeq$ 350 MeV is achieved.

hep-ph↗

arXiv2007

Colour Modification of Effective T-odd Distributions

We show that soft-gluon twist-3 contributions to single-spin asymmetries (SSA) in hard processes may be expressed in the form of effective T-odd Sivers distributions, whose signs and scales are modified by process-dependent colour factors. We thus prove that the Sivers mechanism may also be applied at large transverse momenta. We stress that twist-3 SSA in semi-inclusive deeply inelastic scattering and Drell-Yan processes are suppressed by transverse momentum rather than a virtual-photon momentum transfer and thus naively correspond to twist two at the hadronic level. More rigorously, the transverse-momentum weighted averages of the Sivers function correspond to increasing twist (3, 5, 7, ...) while the full kT-dependent Sivers function (just as other transverse-momentum dependent distribution and fragmentation functions) corresponds to a resummed infinite tower of higher twists.

hep-ph↗

arXiv2002

Bjorken sum rule at low Q^2

A description of the generalized Gerasimov-Drell-Hearn sum rules for proton and neutron is suggested, using their relation to the Bjorken sum rule. The results support an earlier conjecture, that the structure function g_T features a smooth Q^2-dependence, while the structure function g_2 is changing rapidly, due to the elastic contribution to the Burkhardt-Cottingham sum rule. A possible violation of this later sum rule is briefly discussed.

hep-ph↗