O. P. Solovtsova

Adler function for light quarks in analytic perturbation theory

The method of analytic perturbation theory, which avoids the problem of ghost-pole-type singularities and gives a self-consistent description of both spacelike and timelike regions, is applied to describe the {open_quotes}light{close_quotes} Adler function corresponding to the nonstrange vector channel of the inclusive decay of the {tau} lepton. The role of threshold effects is investigated. The behavior of the quark-antiquark system near threshold is described by using a new relativistic resummation factor. It is shown that the method proposed leads to good agreement with the {open_quotes}experimental{close_quotes} Adler function down to the lowest energy scale.

Analytic perturbation theory and inclusive τ decay

Abstract We apply analytic perturbation theory to the inclusive decay of a τ lepton into hadrons. It is shown that the resulting analyticity of the coupling constant strongly influences the value of the QCD Λ-parameter extracted from the experimental data on τ decay.

Four-loop QCD analysis of the Bjorken sum rule

Abstract We study the polarized Bjorken sum rule (BSR) at low momentum transfers in the range 0.22 Q 1.73 GeV with the four-loop N3LO expression for the coefficient function C Bj ( α s ) in the framework of the common QCD perturbation theory (PT) and the singularity-free analytic perturbation theory (APT). The analysis of the PT series for C Bj ( α s ) gives a hint to its asymptotic nature manifesting itself in the region Q 1 GeV . It relates to the observation that the accuracy of both the three- and four-loop PT predictions happens to be at the same 10% level. On the other hand, the usage of the two-loop APT allows one to describe the precise low energy JLab data down to Q ∼ 300 MeV and gives a possibility for reliable extraction of the higher twist (HT) corrections. At the same time, above Q ∼ 700 MeV the APT two-loop order with HT is equivalent to the four-loop PT with HT compatible to zero and is adequate to current accuracy of the data.

AN ANALYTIC METHOD OF DESCRIBING R-RELATED QUANTITIES IN QCD

A model based on the analytic approach to QCD, involving a summation of threshold singularities and taking into account the nonperturbative character of the light quark masses, is applied to find hadronic contributions to different physical quantities. It is shown that the suggested model allows us to describe well such objects as the hadronic contribution to the anomalous magnetic moment of the muon, the ratio of hadronic to leptonic τ-decay widths in the vector channel, the Adler D-function, the smeared RΔ-function, and the hadronic contribution to the evolution of the fine structure constant.

Nucleon spin structure and perturbative QCD frontier on the move

We discuss the interplay between higher orders of the perturbative QCD expansion and higher-twist contributions in the analysis of recent Jefferson Lab data on the lowest moments of spin-dependent proton and neutron structure functions Γ1p,n(Q2) and Bjorken sum rule function Γ1p-n(Q2) at 0.05

Analytic perturbation theory: A new approach to the analytic continuation of the strong coupling constant {alpha}{sub S} into the timelike region

The renormalization group applied to perturbation theory is ordinarily used to define the running coupling constant in the spacelike region. However, to describe processes with timelike momenta transfers, it is important to have a self-consistent determination of the running coupling constant in the timelike region. The technique called analytic perturbation theory (APT) allows a consistent determination of this running coupling constant. The results are found to disagree significantly with those obtained in the standard perturbative approach. Comparison between the standard approach and APT is carried out to two loops, and threshold matching in APT is applied in the timelike region. {copyright} {ital 1998} {ital The American Physical Society}

Gross{endash}Llewellyn Smith sum rule in the analytic approach to perturbative QCD

We apply analytic perturbation theory to the Gross{endash}Llewellyn Smith sum rule. We study the Q{sup 2} evolution and the renormalization scheme dependence of the analytic three-loop QCD correction to this sum rule, and demonstrate that the results are practically renormalization scheme independent and lead to rather different Q{sup 2} evolution than the standard perturbative correction possesses. {copyright} {ital 1999} {ital The American Physical Society}

PERTURBATIVE EXPANSIONS IN THE INCLUSIVE DECAY OF THE TAU-LEPTON

A comparative analysis is performed for various forms of perturbative expansions in spacelike and timelike regions. As applied to the inclusive decay of the τ-lepton, comparison is given for the results derived within the framework of the standard perturbation theory and the analytic approach that modernizes perturbative expansions so that the new approximations reflect basic principles of the theory: renormalization invariance, spectrality, and causality. Advantages and self-consistency of the analytic approach in describing τ-lepton decay are demonstrated.

Remark on the perturbative component of inclusiveτdecay

In the context of the inclusive

Role of the analyticity of the QCD coupling constant in the description of the inclusive decay of a τ lepton into hadrons

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