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A. A. Pivovarov

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

At least 55 records · Page 3Linked to original sources
arXiv2017

The production of the $f_1(1285) γ$ and $a_1(1260) γ$ in colliding $e^{+}e^{-}$-beams in threshold domain

The processes $e^{+}e^{-}\!\to\! (f_1(1285), a_1(1260))γ$ in threshold domain are considered in the framework of the extended Nambu--Jona-Lasinio model. The channels with the ground $ρ(770)$, $ω(782)$ and radially excited $ρ(1450)$, $ω(1420)$ intermediate meson states are taken into account. It is shown that in the process $e^{+}e^{-}\to f_1(1285)γ$, the probability of the subprocesses with $ρ$-mesons significantly exceeds the probability of the subprocesses with $ω$-mesons, whereas, in the process $e^{+}e^{-} \to a_1(1260) γ$, $ρ$- and $ω$-channels give approximately equal contributions. The mechanism of this effect is discussed. The radiative decay widths of $ρ(1450)\!\to\! f_{1}(1285)γ$, $ω(1420)\!\to\! f_{1}(1285)γ$, $ρ(1450)\!\to\! a_1(1260)γ$ and $ω(1420)\!\to\! a_1(1260)γ$ are calculated.

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arXiv2017

The decays $τ\rightarrow (η,η') K^{-} ν_τ$ in the extended Nambu-Jona-Lasinio model

The decays $τ\rightarrow (η,η') K^{-} ν_τ$ 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 vector channels, the subprocesses with intermediate $K^{*}(892)$ and $K^{*}(1410)$ mesons play the main role. In the scalar channels, the subprocesses with intermediate $K_{0}^{*}(800)$ and $K_{0}^{*}(1430)$ mesons are taken into account. Scalar channels play a less important role in calculation of the full width of the decay $τ\rightarrow (η,η') K^{-} ν_τ$. The obtained results are in satisfactory agreement with the experimental data.

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arXiv2016

The decay $τ\rightarrow K^{-}π^{0}ν_τ$ in the Nambu-Jona-Lasinio model

In this paper, the width of the decay $τ\rightarrow K^{-}π^{0}ν_τ$ 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 account. It is shown that the main contribution to the width of this decay is given by the subprocesses with the intermediate $W$-boson and vector $K^{*}(892)$ meson. The scalar channel with the intermediate $K_{0}^{*}(800)$ meson gives an insignificant contribution. In Appendix, it is shown that the contribution of the subprocess with the intermediate ${K^{*}}'(1410)$ meson is negligible as well. The obtained results are in satisfactory agreement with the experimental data.

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arXiv2016

The decay $τ\rightarrow K^{0}K^{-}ν_τ$ in the extended Nambu-Jona-Lasinio model

The full and differential widths of the decay $τ\rightarrow K^{0}K^{-}ν_τ$ are calculated in the framework of the extended Nambu-Jona-Lasinio model. The contributions of the subprocesses with the intermediate vector mesons $ρ$(770) and $ρ$(1450) are taken into account. The obtained results are in satisfactory agreement with the experimental data.

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arXiv2016

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 model

The processes $e^{+}e^{-} \rightarrow K^{\pm} K^{*\mp}(892)$ and $e^{+}e^{-} \rightarrow ηϕ(1020)$ are calculated in the framework of the extended Nambu-Jona-Lasinio model. The intermediate vector mesons $ρ(770), ω(782), ϕ(1020)$ and their first radially-excited states are taken into account. The obtained results are in satisfactory agreement with the experimental data. The predictions for the cross sections of the reactions $e^{+}e^{-} \rightarrow K^{\pm} K^{*\mp}(1410)$, $e^{+}e^{-} \rightarrow η^{'}(958) ϕ(1020)$ and $e^{+}e^{-} \rightarrow ηϕ(1680)$ were made.

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arXiv2014

Radial excitations of heavy-light mesons from QCD sum rules

QCD 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 the decay constants of the first radial excitations, $D^{(*)'},D_s^{(*)'}$ and $B^{(*)'},B_s^{(*)'}$, respectively, provided the masses of these resonances are used as an input. For the radially excited charmed mesons we use available experimental data, whereas the masses of analogous bottom mesons are estimated from the heavy-quark limit. The decay constants predicted for the radial excitations of heavy-light pseudoscalar and vector mesons are systematically smaller than those of the ground states and we comment on the possible origin of this difference. Our results can be used in the sum rule calculations of heavy-to-light form factors and in the factorization approximations for nonleptonic $B$-meson decays where the decay constants of charmed mesons enter as input parameters.

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arXiv2013

Understanding perturbative results for decays of τleptons into hadrons

We 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 hadronic τdecays and e^+ e^- annihilation.

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arXiv2012

Calculating loops without loop calculations: NLO computation of pentaquark correlators

We 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 technique is explained in some detail. We present explicit NLO results for several interpolating pentaquark currents that have been written down in the literature. Our modular approach is easily adapted to the case of NLO corrections to multiquark correlators with an arbitrary number of quarks/antiquarks.

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arXiv2010

Charm-loop effect in $B \to K^{(*)} \ell^{+} \ell^{-}$ and $B\to K^*γ$

We 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. The nonfactorizable soft-gluon emission from $c$-quarks is cast in the form of a nonlocal effective operator. The $B\to K^{(*)}$ matrix elements of this operator are calculated from the QCD light-cone sum rules with the $B$-meson distribution amplitudes. As a byproduct, we also predict the charm-loop contribution to $B\to K^*γ$ beyond the local-operator approximation. To describe the charm-loop effect at large $q^2$, we employ the hadronic dispersion relation with $ψ=J/ψ,ψ(2S), ...$ contributions, where the measured $ B\to K^{(*)}ψ$ amplitudes are used as inputs. Matching this relation to the result of QCD calculation reveals a destructive interference between the $J/ψ$ and $ψ(2S)$ contributions. The resulting charm-loop effect is represented as a $q^2$-dependent correction $ΔC_9(q^2)$ to the Wilson coefficient $C_9$. Within uncertainties of our calculation, at $q^2$ below the charmonium region the predicted ratio $ΔC_9(q^2)/C_9$ is $\leq 5% $ for $B\to K \ell^+\ell^-$, but can reach as much as 20% for $B\to K^*\ell^+\ell^-$, the difference being mainly caused by the soft-gluon contribution.

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arXiv2008

Next-to-Leading Order perturbative QCD corrections to baryon correlators in matter

We 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 functions of the vector quark condensate in matter. This condensate appears in matter due to the violation of Lorentz invariance. The NLO perturbative QCD corrections turn out to be large which implies that the NLO corrections must be included in a sum rule analysis of the properties of both bound nucleons and relativistic nuclear matter.

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arXiv2008

Heavy baryon properties with NLO accuracy in perturbative QCD

We 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 mass quark field for a variety of quantum numbers of the baryonic currents. We consider both the massless limit and the HQET limit of the correlator as special cases of the general finite mass formula and find agreement with previous results. We present closed form expressions for the moments of the spectral density. We determine the residues of physical baryon states using sum rule techniques.

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arXiv2007

Towards NNLO Accuracy in the QCD Sum Rule for the Kaon Distribution Amplitude

We calculate the $O(α_s)$ and $O(α_s^2)$ 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 contributions to the sum rule. A complete factorization is implemented, removing logarithms of $s$-quark mass from the coefficients in the operator-product expansion. The sum rule with radiative corrections yields $a_1^K(1 \GeV)=0.10\pm 0.04$.

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arXiv2007

Analyzing B_s - bar B_s mixing: Non-perturbative contributions to bag parameters from sum rules

We 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 operators R_2 and R_3, which appear at next-to-leading order in the 1/m_b expansion. We conclude that the violation of the factorization approximation for these matrix elements due to non-perturbative vacuum condensates is as low as 1-2%.

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arXiv2006

Large next-to-leading order QCD corrections to pentaquark sum rules

Using 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 which makes a standard sum rule analysis problematic. However, the NLO corrections to the correlator in configuration space are reasonable. We discuss the implications of our results for the phenomenological sum rule analysis of pentaquark states.

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arXiv2005

On the evaluation of a certain class of Feynman diagrams in x-space: Sunrise-type topologies at any loop order

We 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 it to be timely to discuss their evaluation from a unified point of view. The method is based on the analysis of the diagrams directly in configuration space which, in the case of the sunrise-type diagrams and diagrams related to them, leads to enormous simplifications as compared to the traditional evaluation of loops in momentum space. We present explicit formulae for their analytical evaluation for arbitrary mass configurations and arbitrary dimensions at any loop order. We discuss several limiting cases of their kinematical regimes which are e.g. relevant for applications in HQET and NRQCD.

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arXiv2004

Disentangling perturbative and power corrections in precision tau decay analysis

Hadronic 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 quark mass from the data on Cabibbo suppressed tau decays. We show that with inclusion of new five-loop perturbative corrections in the analysis the convergence of perturbation theory remains acceptable only for few low order moments. We obtain m_s(M_τ) =130\pm 27 MeV in agreement with previous estimates.

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