Sum rules for B^0 - \bar B^0 mixing at NLO of pQCD
The 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.
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arXiv subjects
A. A. Pivovarov
Publications and source records attributed to A. A. Pivovarov.
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 α_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.
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Laurent series expansion of sunrise-type diagrams using configuration space techniques
We 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. For negative powers of \eps the results are obtained in analytical form. For positive powers of \eps including the finite \eps^0 contribution the result is obtained numerically in terms of low-dimensional integrals. We present general features of the calculation and provide exemplary results up to five loop order which are compared to available results in the literature.
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Determination of the mass of the LambdaLambda dibaryon by the method of QCD sum rules
The method of QCD sum rules is used to calculate the mass of a hypothetical stable dihyperon H with the quantum numbers of two Lambda hyperons, whose existence was predicted by R.L. Jaffe [Phys. Rev. Lett. 31, 195, 617(E) (1977)] in the framework of the MIT quark-bag model. Within the accuracy of the method of QCD sum rules, which in the present case is 20%, the results obtained here agree with those of Jaffe. However, the method of sum rules does not make it possible to determine whether the mass of the dihyperon H lies above or below the Lambda Lambda threshold (i.e., whether H is stable).
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B0 - anti-B0 mixing beyond factorization
We present a calculation of the B0 - anti-B0 mixing matrix element in the framework of QCD sum rules for three-point functions. We compute alpha_s corrections to a three-point function at the three-loop level in QCD perturbation theory, which allows one to extract the matrix element with next-to-leading order (NLO) accuracy. This calculation is imperative for a consistent evaluation of experimentally-measured mixing parameters since the coefficient functions of the effective Hamiltonian for B0 - anti-B0 mixing are known at NLO. We find that radiative corrections violate factorization at NLO; this violation is under full control and amounts to 10%.
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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.
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Heavy mass expansion, light-by-light scattering and the anomalous magnetic moment of the muon
Contributions from light-by-light scattering to (g_μ-2)/2, the anomalous magnetic moment of the muon, are mediated by the exchange of charged fermions or scalar bosons. Assuming large masses M for the virtual particles and employing the technique of large mass expansion, analytical results are obtained for virtual fermions and scalars in the form of a series in (m_μ/M)^2. This series is well convergent even for the case M=m_μ. For virtual fermions, the expansion confirms published analytical formulae. For virtual scalars, the result can be used to evaluate the contribution from charged pions. In this case our result confirms already available numerical evaluations, however, it is significantly more precise.
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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.
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Heavy Quarks on the Lattice
I review the basic ideas behind lattice QCD calculations that involve charm and bottom quarks. I report on the progress in getting the correct hyperfine splitting in charmonium from lattice QCD. Some of the basic technology behind numerical lattice QCD calculations is explained by studying some specific examples: computation of the charm quark mass, and the calculation of fB.
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An interpolation of the vacuum polarization function for the evaluation of hadronic contributions to the muon anomalous magnetic moment
We 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. The model function contains a phenomenological parameter which provides an infrared cutoff to guarantee the smooth behavior of the correlator at the origin in accordance with experimental data in e+ e- annihilation. After fixing a numerical value for this parameter from the leading order hadronic contribution to the muon anomalous magnetic moment the next-to-leading order results related to the vacuum polarization function are accurately reproduced. The properties of the four-point correlator of hadronic electromagnetic currents as for instance the so-called light-by-light scattering amplitude relevant for the calculation of the muon anomalous magnetic moment are briefly discussed.
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Dynamical masses of quarks in quantum chromodynamics
Using Dyson-Schwinger equations we obtain an ultraviolet asymptotics for the dynamical mass of quark in QCD. We also determine a numerical value for the πmeson decay constant f_π.
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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.
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Muon anomalous magnetic moment: a consistency check for the next-to-leading order hadronic contributions
A 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 polarization is rather accurately reproduced in the model. I find a new numerical value for the light-by-light hadronic contribution that leads to agreement with recent experimental result for the muon anomalous magnetic moment.
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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 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.
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Nonleading charmed quark mass corrections to K^0-anti K^0 mixing in the standard model
The nonleading corrections in the inverse mass of the heavy charmed quark to the effective local ΔS=2 Lagrangian of K^0-anti K^0 mixing are calculated within the standard model.
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Spectral moments of two-point correlators in perturbation theory and beyond
We 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 interval [0,M_tau] and the low-energy hadron production in e+ e- annihilation. General arguments are given for the calculability of such moments in perturbation theory using both a finite-order analysis and infinite resummation on the contour. Nonperturbative contributions emerging from the operator product expansion for two-point correlators are discussed within explicit models for the physical spectra. The quantitative analysis strongly disfavours weight functions that suppress the high-energy contribution to theoretical moments. This is in agreement with expectations from qualitative considerations in perturbative QCD with asymptotic freedom. We discuss the implication of our results for the ultimate accuracy that can be reached in tau decays and low-energy e+ e- annihilation into hadrons with present experimental data.
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Vacuum Saturation Hypothesis and QCD Sum Rules
The 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 approach based on sum rules in position (x-)space as elaborated in the paper is relevant and useful tool for the current phenomenology. In particular, it provides the unique possibility of direct non-perturbative estimation of the VEV's of four-quark operators renormalized in any scheme, including the MSbar one.
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Determination of the strange quark mass from Cabibbo-suppressed tau decays with resummed perturbation theory in an effective scheme
We 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 of the tau-system is described by the beta-function of the effective coupling constant and by two gamma-functions for the effective mass parameters of the strange quark in different spin channels. We analyze the stability of our results with regard to high-order terms in the perturbative expansion of the renormalization group functions. A numerical value for the strange quark mass in the MS scheme is extracted m_s(M_τ)=130\pm 27_{exp}\pm 9_{th} MeV. After running to the scale 1 GeV this translates into m_s(1 GeV)=176 \pm 37_{exp}\pm 13_{th} MeV.
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