arXiv subjects

A. A. Pivovarov

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

At least 37 records · Page 2Linked to original sources

arXiv2021

Calculation of the width of the decay $τ\to K^{-} K^{0} ν_τ$ in the extended NJL model with estimation of the contribution of the kaon final state interaction

The branching fraction of the decay $τ\to K^{-} K^{0} ν_τ$ is calculated in the framework of the extended Nambu--Jona-Lasinio model. The contact and vector channels are considered. The contributions to this process of the $ρ$ meson in the ground and first radially excited states are taken into account in the vector channel. The obtained results are in satisfactory agreement with the experimental data. Taking into account the kaon interaction in the final state results in insignificant corrections, which are not beyond the scope of the model uncertainties.

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arXiv2021

$1/N_c$ approximation and universality of vector mesons

In this work, we argue that the observed differences in the value of the vector coupling constant extracted from the decays $ρ\to ππ$ ($g_ρ = 6.0$), $ρ\to l^+l^-$ ($g_ρ = 5.0 $) and $ω\to l^+ l^-$ ($g_ρ = 5.7$), where $l=e,μ$, are an indication of the important role played by the $1/N_c$ corrections in the description of these processes. We show that an emission of a photon by charged meson loops in the $ρ^0, ω,ϕ\toγ$ transitions is a key process that allows to describe above vector meson decays into two leptons with a single value $g_ρ= 6.0$. Our result supports the idea of universality of neutral vector mesons and clarifies the role of accounting of $1/N_c$ corrections to its fulfilment.

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arXiv2021

The second-class current decays $τ\to πη(η') ν_τ$ in the NJL model including the interaction of mesons in the final state

The effect of the interaction of mesons in the final state is additionally considered within the description of $τ\to πη(η') ν_τ$ decays. This interaction is taken into account at the level of production of intermediate pions. One of them, in turn, might be transited into $η$ or $η'$ mesons. Our results do not exceed the experimentally established branching fractions, and they are in agreement with the results of other theoretical studies.

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arXiv2021

The decay $τ\to K^{-} ην_τ$ in the extended Nambu-Jona-Lasinio model taking into account the meson interaction in the final state

The branching fraction of the decay $τ\to K^{-} ην_τ$ has been calculated by using the extended Nambu-Jona-Lasinio model taking into account the meson interaction in the final state. The contact term and the channel with the intermediate ground $K^{*}(892)$ and first radially excited state $K^{*}(1410)$ have been calculated. For the purpose of describing the meson interaction in the final state, the triangle diagram with three mesons has been considered. The cutoff parameter of divergent integrals of the meson loop is equal to the appropriate parameter used in our previous work to describe the decay $τ\to K^{-} π^{0} ν_τ$. Thereby, the present work does not set any additional arbitrary parameters. The obtained results are in satisfactory agreement with the experimental data.

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arXiv2021

Master Integrals for Inclusive Weak Decays of Heavy Flavours at Next-to-Leading Order

We present analytical results for master integrals emerging in the computation of differential rates for inclusive weak decays of heavy flavors at next-to-leading order (NLO) in QCD. As an immediate physical application, these master integrals allow for a calculation of the spectra of the leptonic invariant mass in inclusive semileptonic decays in the framework of the heavy quark expansion, including the NLO QCD corrections to power suppressed terms.

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arXiv2021

The Heavy Quark Expansion for the Charm Quark

We show that one can re-arrange the Heavy Quark Expansion for inclusive weak decays of charmed hadrons in such a way that the resulting expansion is an expansion in $Λ_{\rm QCD} / m_c$ and $α_s (m_c)$ with order-one coefficients. Unlike in the case of the bottom quark, the leading term includes not only the contribution of the free-quark decay, but also a tower of terms related to matrix elements of four quark operators.

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arXiv2020

Fixing the vector coupling constant $g_ρ= 5.0$ in the NJL model and final-state interactions in processes $ρ\to e^+e^-[μ^+μ^-]$, $ρ\to π^+π^-$, $τ\to π^-π^0ν_τ$, and $e^+e^-\toπ^+π^-$

The possibility to use the width of the decay $ρ\to e^{+}e^{-}$ to fix the input parameter $g_ρ=5.0$ of the $SU(2) \times SU(2)$ chiral-symmetric Nambu--Jona-Lasinio model is discussed. It is shown that for a consistent simultaneous description of the processes $ρ\to e^{+}e^{-}$, $ρ\to π^{+}π^{-}$, $τ^{-} \to π^{-}π^{0} ν_τ$, and $e^{+}e^{-} \to π^{+}π^{-}$ can be constructed. Taking into account the interaction of pions in the final state appears to be important. The obtained theoretical results for the considered processes are in a satisfactory agreement with experimental data.

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arXiv2020

Processes $τ^- \to π^- π^0 ν_τ$ and $e^{+}e^{-} \to π^{+} π^{-}$ in the chiral NJL model with final state interactions taken into account

The processes $τ^- \to π^- π^0 ν_τ$ and $e^{+}e^{-} \to π^{+} π^{-}$ are considered within the chiral Nambu--Jona-Lasinio model with taking into account the pion final state interactions beyond the leading $1/N_c$ approximation. The contribution of the loop correction caused by a $ρ$ meson exchange between the pions, which gives the main contribution in the P-wave channel, is caclulated. The results for both processes are in a satisfactory agreement with experimental data.

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arXiv2020

On the mixing angle of the vector mesons $ω(782)$ and $ϕ(1020)$

In the present work, the mixing angle of the vector $ω(782)$ and $ϕ(1020)$ mesons is estimated in the framework of Nambu--Jona-Lasinio model. The decay $ϕ\to π^{0} γ$ is considered as a basic process to determine this angle. The obtained value is compared with the results of the other authors. Besides, the width of the decay $ϕ\to 3π$ and the cross-section of the process $e^{+}e^{-} \to π^{0} ϕ$ are calculated by using this angle.

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arXiv2020

Account for axial vector mesons in the $η\toπ^+π^-γ$ and $η' \toπ^+π^-γ$ decays

The rates and spectra of the anomalous $η\toπ^+π^-γ$ and $η' \toπ^+π^-γ$ decays are calculated. The approach is based on the effective meson Lagrangian obtained in the Nambu-Jona-Lasinio model with vector and axial-vector mesons by integrating out quark fields. The resulting action is affected by mixing between members of pseudoscalar $J^{PC}=0^{-+}$ and axial-vector $1^{++}$ nonets that violates some low-energy theorems. In this note we point out that a gauge covariant procedure to diagonalize this mixing allows for consistent description of the $η\toπ^+π^-γ$ and $η' \toπ^+π^-γ$ decays.

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arXiv2019

The decay $τ\to K^{*0}(892) K^- ν_τ$ in the extended NJL model

In the extended Nambu -- Jona-Lasinio model, the decay width of $τ\to K^{*0}(892) K^- ν_τ$ is calculated. The contributions from the contact diagram and diagrams with intermediate axial-vector, vector and pseudoscalar mesons in the ground and first radially excited states are taken into account. It is shown that axial-vector and vector channel with a contact diagram give a dominant contribution to the decay width. The obtained results for the decay width $τ\to K^{*0}(892) K^- ν_τ$ are in satisfactory agreement with experimental data. A prediction for differential distribution over the invariant mass of the meson pair $K^{*0}(892) K^-$ is given.

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arXiv2019

The decay $τ\to K^{*-}(892) ην_τ$ in the NJL model

The decay width $τ\to K^{*-}(892) ην_τ$ was calculated in the Nambu--Jona-Lasinio model. Four channels were taken into account: the contact channel (the final states are directly producted from lepton current without any intermediate meson states), the axial-vector channel with two intermediate physical states $K_{1}(1270)$ and $K_{1}(1400)$, the vector channel with intermediate $K^{*}(892)$ meson and the pseudoscalar channel with intermediate $K$ meson. It is shown that the first two channels give the dominant contribution to the decay width. Of the remaining two channels, the pseudoscalar channel plays a more prominent role. The final result is in satisfactory agreement with experimental data. Prediction for the differential decay width is presented.

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arXiv2019

The decays $τ\to [ω(782), ϕ(1020)] K^{-} ν_τ$ in the extended NJL model

In the extended Nambu--Jona-Lasinio model, the decay widths of the processes $τ\to [ω(782), ϕ(1020)] K^{-} ν_τ$ were calculated. The intermediate channels with axial vector ($K_{1}(1270)$, $K_{1}(1400)$ and $K_{1}(1650)$), vector ($K^{*}(892)$ and $K^{*}(1410)$) and pseudoscalar ($K$ and $K(1460)$) mesons were considered. The results for these processes are in satisfactory agreement with the experimental data.

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arXiv2018

Decay rates $f_{1}(1285)\to ρ^{0}π^{+} π^{-}$ and $a_{1}(1260)\toωπ^{+}π^{-}$ in the Nambu -- Jona-Lasinio model

The anomalous decays $f_1(1285)\toρ^0π^+π^-$ and $a_1(1260)\toωπ^+π^-$ violating natural parity for vectors and axial-vectors are studied in the framework of the Nambu -- Jona-Lasinio model. We consider the Lagrangian with $U(2)_L\times U(2)_R$ chiral symmetric four quark interactions. The theory is bosonized and corresponding effective meson vertices are obtained in the leading order of $1/N_c$ and derivative expansions. The uncertainties related with the surface terms of anomalous quark triangle diagrams are fixed by the corresponding symmetry requirements. We make a numerical estimate of the decay widths $Γ(f_1(1285)\toρ^0π^+π^-)=2.78\, \mbox{MeV}$ and $Γ(a_1(1260)\toωπ^+π^-)=87\, \mbox{keV}$. Our result on the $f_1(1285)\toρ^0π^+π^-$ decay rate is in a good agreement with experiment. It is shown that a strong suppression of the $a_1(1260)\toωππ$ decay is a direct consequence of destructive interference between box and triangle anomalies.

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arXiv2018

$τ\to f_1 (1285)π^{-} ν_τ$ decay in the extended Nambu -- Jona-Lasinio model

Within the framework of the extended Nambu -- Jona-Lasinio model, we calculate the matrix element of the $τ\to f_1(1285) π^{-} ν_τ$ decay, obtain the invariant mass distribution of the $f_1π$ -system and estimate the branching ratio Br$(τ\to f_1 π^{-}ν_τ)=4.0\times 10^{-4}$. The two types of contributions are considered: the contact interaction, and the axial-vector $I^G(J^{PC})=1^-(1^{++})$ resonance exchange. The latter includes the ground $a_1(1260)$ state, and its first radially excited state, $a_1(1640)$. The corrections caused by the $π-a_1$ transitions are taken into account. Our estimate is in a good agreement with the latest empirical result Br$(τ\to f_1 π^{-} ν_τ)=(3.9\pm 0.5)\times 10^{-4}$. The distribution function obtained for the decay $τ\to f_1(1285) π^{-} ν_τ$ shows a clear signal of $a_1(1640)$ resonance which should be compared with future experimental data including our estimate of the decay width $Γ(a_1(1640) \to f_1 π)=14.1\,\mbox{MeV}$.

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arXiv2018

Low energy process $e^{+}e^{-} \rightarrow K^{+} K^{-}$ in the extended Nambu-Jona-Lasinio model

In 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 pairs $K^{+}$ $K^{-}$ are generated by an intermediate photon, and processes with intermediate vector mesons $ρ$, $ω$ and $ϕ$ in the ground and in the first radially excited states. The results obtained here are compared with experimental data recently received in Novosibirsk and in Stanford.

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arXiv2017

$O(α_s)$ corrections to the correlator of finite mass baryon currents

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 limit of the correlator from the general formula as particular cases. We also give explicit expressions for the moments of the spectral density.

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arXiv2017

The anomalous decay $f_1(1285)\toργ$ and related processes

We work out the low-energy expansion of the anomalous $f_1(1285)\toργ$ 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 $f_1(1285)\toωγ$, $a_1(1260)\toωγ$, and $a_1(1260)\toργ$, are also considered. An effective meson Lagrangian responsible for $f_1ργ$, $f_1ωγ$, $a_1ργ$ and $a_1ωγ$ interactions is found. The predicted radiative decay widths, $Γ_{f_1\toρ^0γ}=311\ \mbox{keV}$, $Γ_{f_1\toωγ}=34.3\ \mbox{keV}$, $Γ_{a_1\toρ^0γ}=26.8\ \mbox{keV}$, $Γ_{a_1\toωγ}=238\ \mbox{keV}$, allow an experimental test of the hypothesis that $f_1(1285)$ and $a_1(1260)$-mesons have a quark-antiquark nature. At present, only the $f_1(1285)\toργ$ decay has been measured. Our result is in remarkably good agreement with the recent data of CLAS Collaboration $Γ_{f_1\toρ^0γ}=453\pm 177\ \mbox{keV}$, but disagrees with the PDG-based estimate of $Γ_{f_1\toρ^0γ}=1326\pm 313\ \mbox{keV}$. The calculations presented require a minimum of theoretical input, and are shown to be consistent with the non-renormalization theorems of QCD.

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