Local duality for the ρ\rho-meson width revisited

Local duality estimates for the $\rho$-meson leptonic width and the spectrum of radial excitations are updated. New perturbative corrections are included in the analysis that gives good agreement with experimental data on low energy resonances.Comment: 10 pages, Late

COMPUTATION OF COEFFICIENT FUNCTIONS FOR AN EXPANSION OF PARAPOSITRONIUM DECAY WIDTH USING REDUCE

A kind of asymptotic expansion for calculation of the (para)positronium decay rate is formulated. The method is completely relativistic and gauge invariant. The expansion goes over the inverse square of relative momentum $k$ of two photons in Euclidean region and the actual width is determined at $k^2=-m^2$, $m$ being the electron mass.Comment: Latex fil

On the nonrelativistic dynamics of heavy particles near the production threshold

A solution to the Schrodinger equation for the nonrelativistic Green function which is used for describing the heavy quark-antiquark pair production near the threshold in $e^+e^-$ annihilation is presented. A quick comparison with existing results is given. A choice of the effective mass scale for the nonrelativistic system with Coulomb interaction is discussed.Comment: 12 pages, late

Determination of the numerical value for the strong coupling constant from tau decays in perturbative QCD

The determination of the numerical value for the strong coupling constant from tau decays in perturbative QCD is briefly described. Main emphasis is made on the use of the renormalization scheme invariance of the theory for reducing uncertainties related to truncation of the series in the strong coupling constant. The analysis of the convergence of the series is presented and the possibility of the asymptotic growth at the NNNLO is discussed.Comment: Talk given at 15th International Seminar ``Quarks-2002'', Novgorod the Great, Russia, June 1-7, 2002, latex, 14 page

Heavy quark production near the threshold in QCD

Theoretical results for the cross section of heavy quark production near the threshold at NNLO of NRQCD are briefly overviewed.Comment: Talk given at 10th Lomonosov conference on Elementary Particle Physics, August 2001, Moscow, Russia, 9 pages, Late

Mixing of neutral B mesons and factorization

A brief review of checking the factorization hypothesis for matrix element of $B^0 - \bar B^0$ mixing within operator product expansion and QCD sum rules is given. Both perturbative and power corrections are considered.Comment: LaTeX file, 7 page

Renormalization group analysis of the tau-lepton decay within QCD

A technique to sum up the regular corrections appearing under the analytic continuation from the spacelike momentum region to the timelike one is proposed. A perturbative part of the inclusive semileptonic decay width of the tau-lepton in analyzed in detail.Comment: Electronic version of the published paper, latex, 6 page

Computing non-factorizable pQCD corrections to hadronic B^0 - \bar B^0 mixing matrix element within sum rules technique for three point Green functions

In this talk I report on the results of a recent calculation of the \alpha_s corrections to a three-point correlation function at the three-loop level in QCD perturbation theory, which allows one to extract the matrix element of B^0 -\bar B^0 mixing with next-to-leading order accuracy. The evaluation of mixing parameter at NLO allows for a consistent analysis of B^0 -\bar B^0 mixing since the coefficient functions of the effective Hamiltonian for this process are known with the necessary accuracy.Comment: 10 pages, Latex, 4 figures, Q-2004 tal

High order PT calculations for heavy quarks near threshold

Results of analytical calculations for heavy quark systems in higher orders of perturbation theory are overviewed. I discuss baryons with one finite mass quark in the next-to-leading order and heavy quark pair production near the threshold within NRQCD.Comment: 14 pages, latex, 1 figure. Talk given at Research Workshop ``Calculations for Modern and Future Colliders'', JINR, Dubna, Russia, July 9-23, 200

Analytical results for e+e−→ttˉe^+e^-\to t\bar t and γγ→ttˉ\gamma\gamma\to t\bar t observables near the threshold up to the next-to-next-to-leading order of NRQCD

We present an analytical description of top-antitop pair production near the threshold in $e^+e^-$ annihilation and \g\g collisions. A set of basic observables considered includes the total cross sections, forward-backward asymmetry and top quark polarization. The threshold effects relevant for the basic observables are described by three universal functions related to S wave production, P wave production and S-P interference. These functions are computed analytically up to the next-to-next-to-leading order of NRQCD. The total $e^+e^-\to t\bar t$ cross section near the threshold is obtained in the next-to-next-to-leading order in the closed form including the contribution due to the axial coupling of top quark and mediated by the Z-boson. The effects of the running of the strong coupling constant and of the finite top quark width are taken into account analytically for the P wave production and S-P wave interference.Comment: 46 pages LaTeX, editorial change