Results for "A. A. Pivovarov"

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Muon anomalous magnetic moment: a consistency check for the next-to-leading order hadronic contributionsOct 18 2001A model for verifying a consistency of the next-to-leading order hadronic contributions to the muon anomalous magnetic moment with those of the leading order is proposed. A part of the next-to-leading order hadronic contributions related to the vacuum ... More
Spectrality, coupling constant analyticity and the renormalization groupApr 21 2001Analytic structure in the strong coupling constant that emerges for some observables in QCD after duality averaging of renormalization group improved amplitudes is discussed. It is shown that perturbation theory calculations are justified for the proper ... More
High order PT calculations for heavy quarks near thresholdSep 10 2000Results 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. ... More
Sum rules for B^0 - \bar B^0 mixing at NLO of pQCDOct 04 2004The matrix element of B^0 -\bar B^0 mixing is evaluated from QCD sum rules for three-point correlators with next-to-leading order accuracy in pQCD.
Determination of the numerical value for the strong coupling constant from tau decays in perturbative QCDJan 12 2003The 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 ... More
Analytical continuation and resummed perturbation theoryAug 26 1997A pattern of partial resummation of perturbation theory series inspired by analytical continuation is discussed for some physical observables.
On the nonrelativistic dynamics of heavy particles near the production thresholdNov 27 1999A 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 ... More
Two-loop corrections to the correlator of tensor currents in gluodynamicsMay 26 1999Results of evaluating the leading order $\alpha_s$ corrections to the correlator of tensor currents in pure gluodynamics are presented. These corrections to the parton result for the correlator are not large numerically that allows one to use perturbation ... More
$t\bar t$ cross section near the production threshold in NNLO of NRQCDSep 04 2000The cross section near the $t\bar t$ production threshold in $e^+e^-$ annihilation and $\gamma\gamma$ collisions is discussed. The NNLO results within NRQCD are briefly overviewed.
Renormalization group analysis of the tau-lepton decay within QCDFeb 01 2003A 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 ... More
Running electromagnetic coupling constant: low energy normalization and the value at M_ZNov 09 2000A numerical value for the running electromagnetic coupling constant in the MS scheme is calculated at the low energy normalization scale equal to the tau-lepton mass M_\tau. This low energy boundary value is used for running the electromagnetic coupling ... More
Mixing of neutral B mesons and factorizationJun 29 1996A 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.
Computing non-factorizable pQCD corrections to hadronic B^0 - \bar B^0 mixing matrix element within sum rules technique for three point Green functionsSep 22 2004In 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 ... More
Heavy quark production near the threshold in QCDOct 31 2001Theoretical results for the cross section of heavy quark production near the threshold at NNLO of NRQCD are briefly overviewed.
Local duality for the $ρ$-meson width revisitedDec 29 1997Local 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.
Extraction of the strong coupling constant and strange quark mass from semileptonic tau decaysNov 16 2002In this lecture I present a pedagogical introduction to the low-energy phenomenology of light flavors. The renormalization scheme freedom in defining QCD parameters is discussed. It is shown in some details how one can extract an accurate numerical value ... More
Nonleading charmed quark mass corrections to K^0-anti K^0 mixing in the standard modelJul 29 2001The nonleading corrections in the inverse mass of the heavy charmed quark to the effective local \Delta S=2 Lagrangian of K^0-anti K^0 mixing are calculated within the standard model.
Theoretical uncertainties for weak decays: higher dimension operatorsNov 21 1996A brief review of recent results on computing contributions of higher dimension operators to weak effective $\Delta S=1,2$ hamiltonians for light quarks is presented.
COMPUTATION OF COEFFICIENT FUNCTIONS FOR AN EXPANSION OF PARAPOSITRONIUM DECAY WIDTH USING REDUCEMay 16 1995A 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 ... More
Low-energy gluon contributions to the vacuum polarization of heavy quarksMar 05 2001We calculate a correction to the electromagnetic current induced by a heavy quark loop. The contribution of this correction to the vacuum polarization function appears at the O(alpha_s^3) order of perturbation theory and has a qualitatively new feature ... More
Threshold expansion of Feynman diagrams within a configuration space techniqueMar 13 2000Mar 14 2000The near threshold expansion of generalized sunset-type (water melon) diagrams with arbitrary masses is constructed by using a configuration space technique. We present analytical expressions for the expansion of the spectral density near threshold and ... More
QSSR estimate of the $B_B$ parameter at next-to-leading orderMar 04 1994We compute the leading $\alpha_s$ corrections to the two-point correlator of the $O_{\Delta B=2}$ operator which controls the $B^0 \bar B^0$ mixing. Using this result within the QCD spectral sum rules approach and some phenomenologically reasonable assumptions ... More
Heavy quark induced effective action for gauge fields in the SU(N_c) x U(1) model and the low-energy structure of heavy quark current correlatorsMar 29 2001We calculate the low-energy limit of heavy quark current correlators within an expansion in the inverse heavy quark mass. The induced low-energy currents built from the gluon fields corresponding to the initial heavy quark currents are obtained from an ... More
Optimized perturbation theory for bound states: toy model and realistic problemJun 20 1995Within quantum mechanics model we study the problem of resummation of an asymptotic perturbation series for bound state parameters via optimization of the perturbative expansion. A possible application of the method to the positronium lifetime calculation ... More
QCD corrections to inclusive heavy hadron weak decays at $Λ_{\rm QCD}^3 /m_Q^3$Jul 22 2019We present an analytical calculation of the $\alpha_s$ corrections for the coefficient of $\rho_D/m_Q^3$ term in the heavy quark expansion for the inclusive semileptonic decays of heavy hadrons, such as $B \to X_c \ell \bar{\nu}$. The full dependence ... More
Chiral condensates in massless QCD and the $U(1)_A$ boson massAug 19 2019The $U(1)_A$ boson mass is calculated through the phenomenological characteristics of the vacuum related to spontaneous breaking of chiral symmetry in QCD. The mass is determined by the mixed quark-gluon condensate $\langle \bar q G q \rangle$ that emerges ... More
Analytical results for $e^+e^-\to t\bar t$ and $γγ\to t\bar t$ observables near the threshold up to the next-to-next-to-leading order of NRQCDApr 08 1999Oct 10 2001We 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. ... More
Next-to-next-to-leading order relation between $R(e^+e^-\to b\bar b)$ and $Γ_{\rm sl}(b\to clν_l)$ and precise determination of $|V_{cb}|$May 16 1998Oct 30 1998We present the next-to-next-to-leading order relation between the moments of the $\Upsilon$ system spectral density and the inclusive $B$-meson semileptonic width. The perturbative series for the width as an explicit function of the moments is well convergent ... More
Quark-hadron duality for $K^0-\bar{K^0}$ mixingNov 27 1997Long distance contribution to the $K^0-\bar K^0$ mixing is taken into account consistently and the corrections to the naive duality result represented by the famous box diagram are found to be small. Estimates are given in the leading order of the chiral ... More
Numerical analysis of renormalon technique in quantum mechanicsNov 29 1996Jul 14 1997We discuss the ways of extracting a low energy scale of an underlying theory using high energy scattering data. Within an exactly solvable model of quantum mechanics we analyze a technique based on introduction of nonperturbative power corrections accounting ... More
A scalar gluonium contribution to $K\rightarrowππ$ decayJul 17 1995We study a new $K\rightarrow\pi\pi$ decay channel with gluons in intermediate state which is normally neglected within the factorization framework. Both short-distance and long-distance parts of the amplitude are calculated. The chiral Lagrangian approach ... More
Top quark threshold production in $γγ$ collision in the next-to-leading orderOct 27 1998Apr 23 1999The total cross section of the top quark-antiquark pair production near threshold in $\gamma\gamma$ collision is computed analytically up to the next-to-leading order in perturbative and nonrelativistic expansion for general photon helicity. The approximation ... More
On a subtle point of sum rules calculations: toy modelMar 30 1995We consider a two-point correlator in massless $\phi^3$ model within the ladder approximation . The spectral density of the correlator is known explicitly and does not contain any resonances. Meanwhile making use of the standard sum rules technique with ... More
Bottom quark pole mass and $|V_{cb}|$ matrix element from $R(e^+e^-\to b\bar b)$ and $Γ_{sl}(b\to clν_l)$ in the next-to-next-to-leading orderJul 20 1998Mar 19 1999We present a consistent analysis of $\Upsilon$ sum rules and $B$-meson semileptonic width in the next-to-next-to-leading order in the strong coupling constant. The analysis is based on the analytical result for the heavy quark vector current correlator ... More
Practical techniques of QCD vs exact results of solvable modelsDec 30 1996Jul 14 1997We check quantitatively the validity of some popular phenomenological approaches of QCD in simple models. Dispersion sum rules are considered within the ladder approximation of a field-theoretic model with OPE given by ordinary loop diagrams which are ... More
Next-to-next-to-leading order vacuum polarization function of heavy quark near threshold and sum rules for $b \bar b$ systemMar 16 1998Apr 06 1998A correlator of the vector current of a heavy quark is computed analytically near threshold in the next-to-next-to-leading order in perturbative and relativistic expansion that includes $\al_s^2$, $\al_sv$ and $v^2$ corrections in the coupling constant ... More
Comment on ``Next-to-next-to-leading order vacuum polarization function of heavy quark near threshold and sum rules for $b \bar b$ system'' and ``Next-to-next-to-leading order relation between $R(e^+e^-\to b\bar b)$ and $Γ_{\rm sl}(b\to clν_l)$ and precise ... MoreJan 19 1999The most recent recalculation of the two-loop correction to the static quark-antiquark potential gave the numerical value different from the previously known one. We comment on the effect this change produces on the numerical estimates of the bottom quark ... More
Extended analysis of the "penguin" part of $K\toππ$ amplitudeMar 14 1995We make an attempt to clarify the role of the annihilation or "penguin" mode in the description of the $K\rightarrow\pi\pi$ decay within the Standard Model. The attention is concentrated on new operators in the effective $\Delta S=1$ Hamiltonian and the ... More
The decays $τ\rightarrow (η,η') K^{-} ν_τ$ in the extended Nambu-Jona-Lasinio modelFeb 16 2016The decays $\tau \rightarrow (\eta,\eta') K^{-} \nu_{\tau}$ are described in the framework of the extended Nambu-Jona-Lasinio model. Both full and differential widths of these decays are calculated. The vector and scalar channels are considered. In the ... More
The decays $τ\rightarrow (η,η') K^{-} ν_τ$ in the extended Nambu-Jona-Lasinio modelFeb 16 2016Feb 15 2017The decays $\tau \rightarrow (\eta,\eta') K^{-} \nu_{\tau}$ are described in the framework of the extended Nambu-Jona-Lasinio model. Both full and differential widths of these decays are calculated. The vector and scalar channels are considered. In the ... More
Vacuum Saturation Hypothesis and QCD Sum RulesMay 10 2001The accuracy of the vacuum saturation hypothesis is discussed using the examples of vacuum expectation values of four-quark operators and the parameter $B$, which determines the short-distance contribution to the $K^0 - \bar K^0$ mixing. Note added: The ... More
The polarization effects of the process $τ\rightarrow K^{-} π^{0} ν_τ$ in the Nambu--Jona-Lasinio modelSep 25 2016The polarization effects of the processes $\tau \rightarrow K^{-} \pi^{0} \nu_{\tau}$ are described in the framework of the Nambu--Jona-Lasinio model. The intermediate vector meson $K^{*}(892)$ is taken into account. The contribution of these effects ... More
Running coupling at small momenta, renormalization schemes and renormalonsOct 02 1995Nov 18 2000We suggest a method of summing the perturbation theory (PT) asymptotic series related to infrared (IR) renormalons in QCD by using special renormalization schemes in which the running coupling can be integrated over the region of small momenta. For the ... More
Dynamical masses of quarks in quantum chromodynamicsJan 16 2002Using Dyson-Schwinger equations we obtain an ultraviolet asymptotics for the dynamical mass of quark in QCD. We also determine a numerical value for the \pi meson decay constant f_\pi.
Renormalization schemes and renormalonsFeb 12 1996We describe some ways how higher order corrections can reveal themselves if integrated over the infrared region. We show that in different renormalization group (RG) schemes and for some observables one has no factorial divergences. We argue that for ... More
Disentangling perturbative and power corrections in precision tau decay analysisOct 13 2004Hadronic tau decay precision data are analyzed with account of both perturbative and power corrections of high orders within QCD. It is found that contributions of high order power corrections are essential for extracting a numerical value for the strange ... More
Bubble chain resummation and universalityDec 02 1995We propose a parameterization for contributions of an infinite set of diagrams (bubble chains) into physical observables represented as integrals of running coupling constant over the finite region in momentum space. The perturbation theory part of contributions ... More
The processes $e^{+}e^{-} \rightarrow K^{\pm} (K^{*\mp}(892), K^{*\mp}(1410))$ and $e^{+}e^{-} \rightarrow (η, η^{'}(958)) (φ(1020), φ(1680))$ in the extended Nambu-Jona-Lasinio modelAug 01 2016The processes $e^{+}e^{-} \rightarrow K^{\pm} K^{*\mp}(892)$ and $e^{+}e^{-} \rightarrow \eta \phi(1020)$ are calculated in the framework of the extended Nambu-Jona-Lasinio model. The intermediate vector mesons $\rho(770), \omega(782), \phi(1020)$ and ... More
Infrared modified analysis for the $τ$ lepton widthJul 05 1996We argue that accounting for higher order corrections in QCD by integrating a running coupling constant through an infrared region can be most easily done with making use of a scheme without the Landau pole. Within this approach the entire ambiguity of ... More
The decay $τ\rightarrow K^{-}π^{0}ν_τ$ in the Nambu-Jona-Lasinio modelNov 26 2015Nov 11 2016In this paper, the width of the decay $\tau \rightarrow K^{-}\pi^{0}\nu_{\tau}$ is calculated in the framework of the Nambu-Jona-Lasinio model. The contributions of the intermediate vector $K^{*}(892)$ and scalar $K_{0}^{*}(800)$ mesons are taken into ... More
The decay $τ\rightarrow K^{0}K^{-}ν_τ$ in the extended Nambu-Jona-Lasinio modelMar 21 2016Nov 11 2016The full and differential widths of the decay $\tau \rightarrow K^{0}K^{-}\nu_{\tau}$ are calculated in the framework of the extended Nambu-Jona-Lasinio model. The contributions of the subprocesses with the intermediate vector mesons $\rho$(770) and $\rho$(1450) ... More
Inclusive weak decays of heavy hadrons with power suppressed terms at NLOJun 26 2015Within the heavy quark expansion techniques for the heavy hadron weak decays we analytically compute the coefficient of the power suppressed dimension five chromo-magnetic operator at next-to-leading order of QCD perturbation theory with the full dependence ... More
Hadronic contributions to the muon anomalous momentSep 05 2019We analyze hadronic contributions to the muon anomalous magnetic moment at NLO. Using the LO result based on scattering data we compute the NLO contributions and, most importantly, the value of the light-by-light term.
New Algebra of Local Symmetries for Regge Limit of Yang-Mills TheoriesMar 12 1998Local effective action is derived to describe Regge asymptotic of Yang-Mills theories. Local symmetries of the effective action originating from the gauge symmetry of the underlying Yang-Mills theory are studied. Multicomponent effective action is introduced ... More
Inclusive semileptonic B decays from QCD with NLO accuracy for power suppressed termsMay 20 2014We present the results of a calculation of the perturbative QCD corrections for the semileptonic inclusive width of a heavy flavored meson. Within the Heavy Quark Expansion we analytically compute the QCD correction to the coefficient of power suppressed ... More
The production of the $f_1(1285) γ$ and $a_1(1260) γ$ in colliding $e^{+}e^{-}$-beams in threshold domainJun 04 2017Jul 09 2017The processes $e^{+}e^{-}\!\to\! (f_1(1285), a_1(1260))\gamma$ in threshold domain are considered in the framework of the extended Nambu--Jona-Lasinio model. The channels with the ground $\rho(770)$, $\omega(782)$ and radially excited $\rho(1450)$, $\omega(1420)$ ... More
$τ\to f_1 (1285)π^{-} ν_τ$ decay in the extended Nambu -- Jona-Lasinio modelJan 09 2018Mar 28 2018Within the framework of the extended Nambu -- Jona-Lasinio model, we calculate the matrix element of the $\tau \to f_1(1285) \pi^{-} \nu_{\tau}$ decay, obtain the invariant mass distribution of the $f_1\pi$ -system and estimate the branching ratio Br$(\tau ... More
Decay rates $f_{1}(1285)\to ρ^{0}π^{+} π^{-}$ and $a_{1}(1260)\toωπ^{+}π^{-}$ in the Nambu -- Jona-Lasinio modelMay 28 2018The anomalous decays $f_1(1285)\to\rho^0\pi^+\pi^-$ and $a_1(1260)\to\omega\pi^+\pi^-$ violating natural parity for vectors and axial-vectors are studied in the framework of the Nambu -- Jona-Lasinio model. We consider the Lagrangian with $U(2)_L\times ... More
Coulomb resummation for $b \bar b$ system near threshold and precision determination of $\al_s$ and $m_b$.Jan 20 1998Apr 05 1998We analyze sum rules for the $\Upsilon$ system with resummation of threshold effects on the basis of the nonrelativistic Coulomb approximation. We find for the pole mass of the bottom quark $m_b=4.75\pm 0.04 GeV$ and for the strong coupling constant $\al_s(M_Z)=0.118\pm ... More
The anomalous decay $f_1(1285)\toργ$ and related processesMay 16 2017Aug 20 2017We work out the low-energy expansion of the anomalous $f_1(1285)\to\rho\gamma$ decay amplitude by using the Nambu--Jona-Lasinio model with $U(2)\times U(2)$ chiral symmetric four-quark interactions in the one-quark-loop approximation. The related processes ... More
Charm-loop effect in $B \to K^{(*)} \ell^{+} \ell^{-}$ and $B\to K^*γ$Jun 25 2010Sep 13 2010We calculate the long-distance effect generated by the four-quark operators with $c$-quarks in the $B\to K^{(*)} \ell^+\ell^-$ decays. At the lepton-pair invariant masses far below the $\bar{c}c$-threshold, $q^2\ll 4m_c^2$, we use OPE near the light-cone. ... More
Two-loop calculations for the propagators of gluonic currents. ErratumDec 11 1996This is an erratum to the paper published in Nucl. Phys. B198(1982)508.
Radial excitations of heavy-light mesons from QCD sum rulesApr 23 2014Jul 18 2014QCD sum rules are commonly used to predict the characteristics of ground-state hadrons. We demonstrate that two-point sum rules for the decay constants of charmed ($D^{(*)},D_s^{(*)}$) and bottom ($B^{(*)},B_s^{(*)}$) mesons can also be modified to estimate ... More
Towards NNLO Accuracy in the QCD Sum Rule for the Kaon Distribution AmplitudeDec 18 2007We calculate the $O(\alpha_s)$ and $O(\alpha_s^2)$ gluon radiative corrections to the QCD sum rule for the first Gegenbauer moment $a_1^K$ of the kaon light-cone distribution amplitude. The NNL0 accuracy is achieved for the perturbative term and quark-condensate ... More
An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic momentNov 16 2001Jul 16 2002We propose a simple parameterization of the two-point correlator of hadronic electromagnetic currents for the evaluation of the hadronic contributions to the muon anomalous magnetic moment. The parameterization is explicitly done in the Euclidean domain. ... More
Next-to-Leading Order perturbative QCD corrections to baryon correlators in matterMay 23 2008Oct 08 2008We compute the next-to-leading order perturbative QCD corrections to the correlators of nucleon interpolating currents in relativistic nuclear matter. The main new result is the calculation of the O(alpha_s) perturbative corrections to the coefficient ... More
Analyzing B_s - bar B_s mixing: Non-perturbative contributions to bag parameters from sum rulesMar 22 2007We use QCD sum rules to compute matrix elements of the Delta B=2 operators appearing in the heavy-quark expansion of the width difference of the B_s mass eigenstates. Our analysis includes the leading-order operators Q and Q_S, as well as the subleading ... More
Large next-to-leading order QCD corrections to pentaquark sum rulesMar 27 2006Jul 18 2006Using configuration space techniques, we calculate next-to-leading order (NLO) five-loop QCD corrections to the correlators of interpolating pentaquark currents in the limit of massless quarks. We obtain very large NLO corrections to the spectral density ... More
On the evaluation of sunset-type Feynman diagramsJun 18 1998Apr 05 2000We introduce an efficient configuration space technique which allows one to compute a class of Feynman diagrams which generalize the scalar sunset topology to any number of massive internal lines. General tensor vertex structures and modifications of ... More
The decays $τ\to [ω(782), φ(1020)] K^{-} ν_τ$ in the extended NJL modelJul 07 2019In the extended Nambu--Jona-Lasinio model, the decay widths of the processes $\tau \to [\omega(782), \phi(1020)] K^{-} \nu_{\tau}$ were calculated. The intermediate channels with axial vector ($K_{1}(1270)$, $K_{1}(1400)$ and $K_{1}(1650)$), vector ($K^{*}(892)$ ... More
Resummation analysis of the $τ$ decay width using the four-loop $β$-functionMar 07 1997Jul 08 1997We extract the strong coupling constant $\alpha_s(m_\tau^2)$ from the semileptonic $\tau$ decay width taking into account resummation effects from the running of the strong coupling constant. In the $\overline{\rm MS}$ scheme the result reads $\alpha_s=0.375\pm ... More
Understanding perturbative results for decays of τleptons into hadronsDec 21 2012May 29 2013We review some results obtained by us and others concerning the structure of higher order perturbation series in perturbative QCD and their resummation using the renormalization group equation. We illustrate our results by a number of examples involving ... More
Calculating loops without loop calculations: NLO computation of pentaquark correlatorsJul 04 2011Aug 27 2012We compute next-to-leading order (NLO) perturbative QCD corrections to the correlators of interpolating pentaquark currents. We employ modular techniques in configuration space which saves us from the onus of having to do loop calculations. The modular ... More
$O(α_s)$ corrections to the correlator of finite mass baryon currentsNov 17 1999Oct 13 2017We present analytical next-to-leading order results for the correlator of baryonic currents at the three loop level with one finite mass quark. We obtain the massless and the HQET limit of the correlator from the general formula as particular cases. We ... More
Perturbative relations between $e^+e^-$ annihilation and $τ$ decay observables including resummation effectsApr 24 1997By exploiting the analyticity properties of the two-point current-current correlator we obtain numerical predictions for the $e^+e^-$ moments in terms of the $\tau$ decay rate. We perform a partial resummation of the pertinent perturbative series expansion ... More
The decays $τ\rightarrow (K, K(1460))ν_τ$ and the value of the weak decay coefficients ${F}_{K}$ and ${{F}_{{K}^{'}}}$ in the extended NJL modelJun 16 2019In the extended NJL model, the decay widths of $\tau\rightarrow (K, K(1460))\nu_{\tau}$, $(K, K(1460))\rightarrow {\mu}\nu_{\mu}$ are calculated. The contributions from intermediate axial-vector mesons ${K}_{1}(1270)$, ${K}_{1}(1400)$ and the first radially ... More
Heavy baryon properties with NLO accuracy in perturbative QCDJul 14 2008We present an analysis of the static properties of heavy baryons at next-to-leading order in the perurbative expansion of QCD. We obtain analytical next-to-leading order three-loop results for the two-point correlators of baryonic currents with one finite ... More
On the evaluation of a certain class of Feynman diagrams in x-space: Sunrise-type topologies at any loop orderJun 28 2005We review recently developed new powerful techniques to compute a class of Feynman diagrams at any loop order, known as sunrise-type diagrams. These sunrise-type topologies have many important applications in many different fields of physics and we believe ... More
Analytical calculation of heavy baryon correlators in NLO of perturbative QCDSep 19 2000We present analytical next-to-leading order results for the correlator of baryonic currents at the three-loop level with one finite mass quark. We obtain the massless and the HQET limits of the correlator as particular cases from the general formula, ... More
Asymptotic structure of perturbative series for tau lepton observablesSep 02 1999We analyze tau lepton decay observables, namely moments of the hadronic spectral density in the finite energy interval (0,M_\tau), within finite order perturbation theory including \alpha_s^4 corrections. The start of asymptotic growth of perturbation ... More
Determination of the strange quark mass from Cabibbo-suppressed tau decays with resummed perturbation theory in an effective schemeMar 16 2000May 10 2001We present an analysis of the m_s^2-corrections to Cabibbo-suppressed tau lepton decays employing contour improved resummation within an effective scheme which is an essential new feature as compared to previous analyses. The whole perturbative QCD dynamics ... More
Asymptotic structure of perturbative series for $τ$ lepton decay observables: $m_s^2$ correctionsNov 11 1999In a previous paper we performed an analysis of asymptotic structure of perturbation theory series for semileptonic $\tau$-lepton decays in massless limit. We extend our analysis to the Cabibbo suppressed $\Delta S=1$ decay modes of the $\tau$ lepton. ... More
Configuration Space Based Recurrence Relations for Sunset-Type DiagramsMar 19 1999Apr 10 2000We derive recurrence relations for the calculation of multiloop sunset-type diagrams with large powers of massive propagators. The technique is formulated in configuration space and exploits the explicit form of the massive propagator raised to a given ... More
Determining the Strange Quark Mass in Cabibbo Suppressed Tau Lepton DecaysMay 15 1998In this work radiative corrections in the total hadronic decay rate of the tau-lepton and some moments of its differential distributions are studied employing perturbative QCD and the operator product expansion. We calculate quadratic quark mass corrections ... More
A numerical test of differential equations for one- and two-loop sunrise diagrams using configuration space techniquesApr 03 2012Aug 23 2012We use configuration space methods to write down one-dimensional integral representations for one- and two-loop sunrise diagrams (also called Bessel moments) which we use to numerically check on the correctness of the second order differential equations ... More
Strong coupling constant from $τ$ decay within renormalization scheme invariant treatmentFeb 15 2000Nov 27 2000We extract a numerical value for the strong coupling constant \alpha_s from the \tau-lepton decay rate into nonstrange particles. A new feature of our procedure is the explicit use of renormalization scheme invariance in analytical form in order to perform ... More
Laurent series expansion of sunrise-type diagrams using configuration space techniquesMar 11 2004Aug 19 2004We show that configuration space techniques can be used to efficiently calculate the complete Laurent series \eps-expansion of sunrise-type diagrams to any loop order in D-dimensional space-time for any external momentum and for arbitrary mass configurations. ... More
O(alpha_s) corrections to the correlator of finite mass baryon currentsNov 17 1999Apr 20 2000We present analytical next-to-leading order results for the correlator of baryonic currents at the three loop level with one finite mass quark. We obtain the massless and the HQET limit of the correlator from the general formula as particular cases. We ... More
Spectral moments of two-point correlators in perturbation theory and beyondMay 22 2001We discuss the choice of weight functions for the moments of the spectral density for two-point correlators of hadronic currents over a finite energy interval. Of phenomenological relevance is an analysis of the spectra of tau lepton decay on the energy ... More
Transcendental numbers and the topology of three-loop bubblesApr 12 1999We present a proof that all transcendental numbers that are needed for the calculation of the master integrals for three-loop vacuum Feynman diagrams can be obtained by calculating diagrams with an even simpler topology, the topology of spectacles.
On the running electromagnetic coupling constant at $M_Z$Dec 21 1998We present a discussion on how to define the running electromagnetic coupling constant at $M_Z$ or some other intermediate scale as e.g. $m_\Upsilon$. We argue that a natural definition consistent with general requirements of the renormalization group ... More
A new technique for computing the spectral density of sunset-type diagrams: integral transformation in configuration spaceMay 05 1998Apr 05 2000We present a new method to investigate a class of diagrams which generalizes the sunset topology to any number of massive internal lines. Our attention is focused on the computation of the spectral density of these diagrams which is related to many-body ... More
Low energy process $e^{+}e^{-} \rightarrow K^{+} K^{-}$ in the extended Nambu-Jona-Lasinio modelMar 25 2018In the extended Nambu-Jona-Lasinio model, the process of production of charged kaon pair on colliding electron-positron beams in the energy interval 1 - 1.7 GeV is described. In studying of this process, we take into account the contact terms when the ... More
Production of $ρ(770)$, $η$ pairs in the decays $ρ(1450)\rightarrow ρ(770)η$, $τ\rightarrow ρ(770)ην_τ$, and in the process of $e^{+}e^{-} \rightarrow ρ(770)η$ in the Extended Nambu - Jona-Lasinio modelNov 27 2017Production of $\rho(770)$, $\eta$ pairs at colliding of electron-positron beams and in the decays $\rho(1450)\rightarrow \rho(770)\eta$, $\tau\rightarrow \rho(770)\eta\nu_{\tau}$ is calculated in the framework of the Nambu - Jona-Lasinio model. In the ... More
New high order relations between physical observables in perturbative QCDMar 01 1997We exploit the fact that within massless perturbative QCD the same Green's function determines the hadronic contribution to the $\tau$ decay width and the moments of the $e^+e^-$ cross section. This allows one to obtain relations between physical observables ... More
Skewed Sudakov Regime, Harmonic Numbers, and Multiple PolylogarithmsDec 18 2018On the example of massless QED we study an asymptotic of the vertex when only one of the two virtualities of the external fermions is sent to zero. We call this regime the skewed Sudakov regime. First, we show that the asymptotic is described with a single ... More
$B^0$-$\bar{B}^0$ mixing: matching to HQET at NNLOJun 01 2018We compute perturbative matching coefficients to the Heavy Quark Effective Theory representation for the QCD effective local $\Delta B=2$ Hamiltonian that determines the mass difference in $B^0-\bar{B}^0$ system of states. We report on the results at ... More
The tetraquark $K_{1}(1400)$ in the decays $τ\to [ω(782), φ(1020)] K^{-} ν_τ$Mar 02 2019Jun 25 2019In the extended Nambu--Jona-Lasinio model, the decay widths of the processes $\tau \to [\omega(782), \phi(1020)] K^{-} \nu_{\tau}$ were calculated. The intermediate strange quark-antiquark mesons in both the ground and the first radially excited states ... More
Decay constants of heavy-light vector mesons from QCD sum rulesMay 23 2013Mar 27 2015We revisit QCD sum rules for the decay constants of heavy-light mesons. In the sum rules for the vector mesons B^*_(s) and D^*_(s) we improve the accuracy of OPE, taking into account the O(alpha_s^2) terms in the perturbative part and calculating the ... More
$B^0-\bar{B}^0$ Mixing at Next-to-Leading OrderJun 20 2016Sep 20 2016We compute the perturbative corrections to the HQET sum rules for the matrix element of the \Delta B=2 operator that determines the mass shift of $B^0$, $\bar{B}^0$ states. Technically, we obtain analytically the non-factorizable contributions at order ... More