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A. A. Pivovarov

Publications and source records attributed to A. A. Pivovarov.

At least 91 records · Page 5Linked to original sources
arXiv2001

Spectrality, coupling constant analyticity and the renormalization group

Analytic 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 observables related to the two-point correlators of hadronic currents the analytic properties of which are well-established. A particular case of gluonic current correlators is discussed in detail.

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arXiv2001

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 correlators

We 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 effective action for gauge fields in the one-loop approximation at the leading order of the 1/m expansion. Explicit formulae for the low-energy spectra of electromagnetic and tensor heavy quark current correlators are given. Consequences of the appearance of a nonvanishing spectral density below the two-particle threshold for high precision phenomenology of heavy quarks are discussed quantitatively.

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arXiv2001

Calculation of the K^0-\bar{K}^0 mixing parameter via the QCD sum rules at finite energies

The QCD finite energy sum rules method is used to show that the parameter of the K^0-\bar{K}_0 mixing \hat{B} is mainly determined by the value of g m_s< \bar{d} G_{μν} σ_{μν} d > and the vacuum expectation values of four-quark operators. Assuming the hypothesis of vacuum dominance and/or unitarity symmetry to estimate latter, it is found that \hat{B}=1.2\pm 0.1. (The updated (March 2001) prediction reads \hat{B} = 1.0 +- 0.1 (for more details, see Comments after the main text).

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arXiv2001

Low-energy gluon contributions to the vacuum polarization of heavy quarks

We 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 -- its absorptive part starts at zero energy in contrast to other contributions where the absorptive parts start at the two-particle threshold. Our result imposes a constraint on the order n of the moments used in the heavy-quark sum rules, n<4.

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arXiv2000

Strong coupling constant from $τ$ decay within renormalization scheme invariant treatment

We extract a numerical value for the strong coupling constant α_s from the τ-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 the actual analysis in a particular renormalization scheme. For the reference coupling constant in the \MSsch-scheme we obtain α_s(M_τ)= 0.3184 \pm 0.0060_{exp} which corresponds to \al_s(M_Z)= 0.1184 \pm 0.0007_{exp} \pm 0.0006_{hq mass}. This new numerical value is smaller than the standard value from $τ$-data quoted in the literature and is closer to \al_s(M_Z)-values obtained from high energy experiments.

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arXiv2000

Running coupling at small momenta, renormalization schemes and renormalons

We 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 method to work, one should consider higher order PT corrections to the standard bubble-chain diagrams. High-order corrections allow one to choose a scheme in which the coupling evolution can smoothly be extrapolated to small momenta. In such schemes the sum of an (extended) IR-renormalon asymptotic series is defined as an integral of the running coupling over the IR region. We give explicit examples of renormalization schemes in QCD which can be used for summing IR-renormalon asymptotic series according to our definition.

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arXiv2000

Running electromagnetic coupling constant: low energy normalization and the value at M_Z

A 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_τ. This low energy boundary value is used for running the electromagnetic coupling constant to larger scales where high precision experimental measurements can be performed. Particular scales of interest are the b-quark mass for studying the Υ-resonance physics and the Z-boson mass M_Z for high precision tests of the standard model and for the Higgs mass determination from radiative corrections. A numerical value for the running electromagnetic coupling constant at M_Z in the on-shell renormalization scheme is also given.

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arXiv2000

Analytical calculation of heavy baryon correlators in NLO of perturbative QCD

We 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, we also give explicit expressions for the moments of the spectral density. Calculations have been performed with an extensive use of the symbolic manipulation programs MATHEMATICA and REDUCE.

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arXiv2000

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.

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arXiv2000

Configuration Space Based Recurrence Relations for Sunset-Type Diagrams

We 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 power. We write down and evaluate a convenient set of basis integrals. The method is well suited for a numerical evaluation of this class of diagrams. We give explicit analytical formulae for the basis integrals in the asymptotic regime.

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arXiv2000

A new technique for computing the spectral density of sunset-type diagrams: integral transformation in configuration space

We 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 phase space in $D$ dimensional space-time. The spectral density is determined by the inverse $K$-transform of the product of propagators in configuration space. The inverse $K$-transform reduces to the inverse Laplace transform in any odd number of space-time dimensions for which we present an explicit analytical result.

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arXiv2000

On the evaluation of sunset-type Feynman diagrams

We 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 the propagators due to particle emission with vanishing momenta can be included with only a little change of the basic technique described for the scalar case. We discuss applications to the computation of $n$-body phase space in $D$-dimensional space-time. Substantial simplifications occur for odd space-time dimensions where the final results can be expressed in closed form through rational functions. We present explicit analytical formulas for three-dimensional space-time.

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arXiv2000

Threshold expansion of Feynman diagrams within a configuration space technique

The 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 compare it with the exact expression obtained earlier using the method of the Hankel transform. We formulate a generalized threshold expansion with partial resummation of the small mass corrections for the strongly asymmetric case where one particle in the intermediate state is much lighter than the others.

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arXiv2000

Top-Antitop Pair Production close to Threshold: Synopsis of recent NNLO Results

Using non-relativistic effective theories, new next-to-next-to-leading order (NNLO) QCD corrections to the total $t\bar t$ production cross section at the Linear Collider have been calculated recently. In this article the NNLO calculations of several groups are compared and the remaining uncertainties are discussed. The theoretical prospects for an accurate determination of top quark mass parameters are discussed in detail. An outlook on possible future improvements is given.

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arXiv1999

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.

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arXiv1999

Asymptotic structure of perturbative series for $τ$ lepton decay observables: $m_s^2$ corrections

In a previous paper we performed an analysis of asymptotic structure of perturbation theory series for semileptonic $τ$-lepton decays in massless limit. We extend our analysis to the Cabibbo suppressed $ΔS=1$ decay modes of the $τ$ lepton. In particular we address the problem of $m_s^2$ corrections to theoretical formulas. The properties of the asymptotic behavior of the finite order perturbation theory series for the coefficient functions of the $m_s^2$ corrections are studied.

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arXiv1999

Asymptotic structure of perturbative series for tau lepton observables

We analyze tau lepton decay observables, namely moments of the hadronic spectral density in the finite energy interval (0,M_τ), within finite order perturbation theory including α_s^4 corrections. The start of asymptotic growth of perturbation theory series is found at this order in a scheme invariant manner. We establish the ultimate accuracy of finite order perturbation theory predictions and discuss the construction of optimal observables.

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