arXiv subjects

A. A. Osipov

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

At least 37 records · Page 2Linked to original sources

arXiv2018

Hadronic electroweak current and $π- a_1$ mixing

It is found that in presence of electroweak interactions the gauge covariant diagonalization of the axial-vector -- pseudoscalar mixing in the effective meson Lagrangian leads to a deviation from the vector meson and the axial-vector meson dominance of the entire hadronic electroweak current. The essential features of such a modification of the theory are investigated in the framework of the extended Nambu-Jona-Lasinio model with explicit breaking of chiral $U(2) \times U(2)$ symmetry. The Schwinger-DeWitt method is used as a major tool in our study of the real part of the relevant effective action. Some straightforward applications are considered.

hep-ph↗

arXiv2018

Precise measurement of $R_{\text{uds}}$ and $R$ between 1.84 and 3.72 GeV at the KEDR detector

The present work continues a series of the KEDR measurements of the $R$ value that started in 2010 at the VEPP-4M $e^+e^-$ collider. By combining new data with our previous results in this energy range we measured the values of $R_{\text{uds}}$ and $R$ at nine center-of-mass energies between 3.08 and 3.72 GeV. The total accuracy is about or better than $2.6\%$ at most of energy points with a systematic uncertainty of about $1.9\%$. Together with the previous precise $R$ measurement at KEDR in the energy range 1.84-3.05 GeV, it constitutes the most detailed high-precision $R$ measurement near the charmonium production threshold.

hep-ex↗

arXiv2018

Thermodynamical properties of strongly interacting matter in a model with explicit chiral symmetry breaking interactions

We analyse the effects of the light and strange current quark masses on the phase diagram of QCD at finite temperature and vanishing baryonic chemical potential, computing the speed of sound, the trace anomaly of the energy momentum tensor and the fluctuations and correlations of the conserved charges associated to baryonic, electric and strangeness numbers. The framework is a known extension of the three flavor Nambu Jona Lasinio model, which includes the full set of explicit chiral symmetry breaking interactions (ESB) up to the same order in large $N_c$ counting as the 't Hooft flavor mixing terms and eight quark interactions. It is shown that the ESB terms are relevant for the description of a soft region in the system's speed of sound and overall slope behavior of the observables computed. At the same time the role of the 8q interactions gets highlighted. The model extension with the Polyakov loop is considered and the results are compared to lattice QCD data.

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arXiv2018

Electromagnetic interactions of mesons induced by the axial-vector -- pseudoscalar mixings

It is shown that the diagonalization of the axial-vector -- pseudoscalar transitions in the effective meson Lagrangian in presence of electromagnetic interactions leads to a deviation from the vector meson dominance picture which usually arises in the Nambu - Jona-Lasinio model. The essential features of such modification of the theory are studied. Some important examples are considered in detail.

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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.

hep-ph↗

arXiv2018

Measurement of $Γ_{ee}\times\mathcal{B}_{μμ}$ for $ψ(2S)$ meson

The product of the electronic width of the $ψ(2S)$ meson and the branching fraction of its decay to the muon pair was measured in the $e^{+}e^{-} \to ψ(2S) \to μ^{+}μ^{-}$ process using nine data sets corresponding to an integrated luminosity of about 6.5 pb$^{-1}$ collected with the KEDR detector at the VEPP-4M electron-positron collider: \[ Γ_{ee}\times\mathcal{B}_{μμ} = 19.3 \pm 0.3 \pm 0.5 ~\text{eV}. \] Adding the previous KEDR results on hadronic and leptonic channels, the values of the $ψ(2S)$ electronic width were obtained under two assumptions: either with the assumption of lepton universality \[ Γ_{ee} = 2.279 \pm 0.015 \pm 0.042 ~\text{keV} \] or without it, summing up hadronic and three independent leptonic channels: \[ Γ_{ee} = 2.282 \pm 0.015 \pm 0.042 ~\text{keV}. \]

hep-ex↗

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 $Γ(a_1(1640) \to f_1 π)=14.1\,\mbox{MeV}$.

hep-ph↗

arXiv2018

Anomalous decay $f_1(1285)\toπ^+π^-γ$ in the Nambu - Jona-Lasinio model

Using the Nambu--Jona-Lasinio model with the $U(2)\times U(2)$ chiral symmetric effective four-quark interactions, we derive the amplitude of the radiative decay $f_1(1285) \toπ^+π^-γ$, find the decay width $Γ(f_1\toπ^+π^-γ)=346\,\mbox{keV}$ and obtain the spectral di-pion effective mass distribution. It is shown that in contrast to the majority of theoretical estimates (which consider the $a_1(1260)$ meson exchange as the dominant one), the most relevant contribution to this process comes out from the $ρ^0$-resonance exchange related with the triangle $f_1ρ^0γ$ anomaly. The spectral function is obtained to be confronted with the future empirical data.

hep-ph↗

arXiv2018

Measurement of $Γ_{ee}(J/ψ)$ with KEDR detector

The product of the electronic width of the $J/ψ$ meson and the branching fractions of its decay to hadrons and electrons has been measured using the KEDR detector at the VEPP-4M $e^+e^-$ collider. The obtained values are: $Γ_{ee}(J/ψ) = 5.550 \pm 0.056 \pm 0.089 \, \text{keV}, $ $Γ_{ee}(J/ψ) \cdot \mathcal{B}_\text{hadrons}(J/ψ) = 4.884 \pm 0.048 \pm 0.078 \, \text{keV}, $ $Γ_{ee}(J/ψ) \cdot \mathcal{B}_{ee}(J/ψ) = 0.3331 \pm 0.0066 \pm 0.0040 \, \text{keV}.$ The uncertainties shown are statistical and systematic, respectively. Using the result presented and the world-average value of the electronic branching fraction, one obtains the total width of the $J/ψ$ meson: $Γ= 92.94 \pm 1.83 \, \text{keV}.$ These results are consistent with the previous experiments.

hep-ex↗

arXiv2017

Mending $ρππ$ vertex through the $πa_1$ diagonalization

The problem of the strong momentum dependence of the $ρππ$-vertex in the extended Nambu -- Jona-Lasinio model is solved by an appropriate choice of fields for spin-1 particles. A corresponding phenomenological Lagrangian is derived. As straightforward applications, the decay widths of $ρ\toππ$, and $a_1\toρπ$ transitions are calculated and compared with known empirical data and previous theoretical estimates.

hep-ph↗

arXiv2017

Strongly Interacting Matter Phase Diagram in the presence of Magnetic Fields in an Extended Effective Lagrangian Approach with Explicit Chiral Symmetry Breaking Interactions

Extensions of the NJL model which go beyond the original 4-quark interaction, which drives the dynamical mass generation, have proven to be quite successful in describing low energy hadronic phenomenology. The inclusion of 8-quark interaction terms solved a metastability problem of the effective potential introduced by the inclusion of the 6-quark 't Hooft determinant term in the 3-flavor version of the model (needed to eliminate the unwanted U(1) axial symmetry) . This model, that has proven to be quite powerful and feature-rich, has been expanded to include all the spin-0 terms, without and with explicit chiral symmetry breaking, which are of the same order as the 't Hooft flavor determinant in a 1/Nc expansion resulting in an unprecedented success in reproducing the low lying scalar and pseudoscalar meson spectra. This success can be seen as a result of the inclusion of the full chiral symmetry breaking pattern. The two critical endpoints which are obtained in the temperature/chemical potential phase diagram are shifted to lower chemical potential and higher temperature when the effect of magnetic field is taken into account. For the studied magnetic field strengths (in the range $eH=0-0.4~GeV^2$) no significant extra transitions are seen to appear.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv2016

Measurement of $R$ between 1.84 and 3.05 GeV at the KEDR detector

Using the KEDR detector at the VEPP-4M $e^+e^-$ collider, we have determined the values of $R$ at thirteen points of the center-of-mass energy between 1.84 and 3.05 GeV. The achieved accuracy is about or better than $3.9\%$ at most of the energy points with a systematic uncertainty less than $2.4\%$.

hep-ex↗

arXiv2016

Light quark mass differences in the $π^0 - η- η'$ system

A generalized 3 flavor Nambu-Jona--Lasinio Lagrangian including the explicit chiral symmetry breaking interactions which contribute at the same order in the large $1/N_c$ counting as the $U_A(1)$ 't Hooft flavor determinant is considered to obtain the mixing angles in the $π^0-η-η'$ system and related current quark mass ratios in close agreement with phenomenological values. At the same time an accurate ordering and magnitude of the splitting of states in the low lying pseudoscalar nonet is obtained.

hep-ph↗

arXiv2015

Measurement of $R_{\text{uds}}$ and $R$ between 3.12 and 3.72 GeV at the KEDR detector

Using the KEDR detector at the VEPP-4M $e^+e^-$ collider, we have measured the values of $R_{\text{uds}}$ and $R$ at seven points of the center-of-mass energy between 3.12 and 3.72 GeV. The total achieved accuracy is about or better than $3.3\%$ at most of energy points with a systematic uncertainty of about $2.1\%$. At the moment it is the most accurate measurement of $R(s)$ in this energy range.

hep-ex↗

arXiv2015

Strange quark matter in the presence of explicit symmetry breaking interactions

It is shown that a first order transition associated with a jump in the strange quark mass appears in a generalized 3 flavour Nambu--Jona-Lasinio (NJL) treatment of quark matter. The generalization of the Lagrangian displays the complete set of spin 0 interactions at leading and subleading orders (LO and NLO) in $\frac{1}{N_c}$counting, including the recently derived NLO explicit chiral symmetry breaking interactions which are of the same order as the 't Hooft flavour determinant. The parameters of the model are tightly constrained by the low energy characteristics in both the pseudoscalar and scalar meson sectors. The transition occurs in a moderate chemical potential region ($μ\simeq 400~\mathrm{MeV}$ for zero temperature) in addition to the usual chiral transition associated with the light quark sector. This feature has at its root the inclusion of the explicit chiral symmetry breaking interactions, which therefore can be seen to act as a catalyst in the production of strange quark matter when compared to the conventional version of the model that takes only into account the 't Hooft interaction in the NLO. It can be traced back to the effect of the interactions which do not violate the Okubo-Zweig-Iizuka rule (OZI), without which the empirical ordering of the scalars ($m_{K^\star}< m_{a_0}\approx m_{f_0}$) is not reproduced.

hep-ph↗

arXiv2015

Nonuniform phases in the 't Hooft extended Nambu--Jona-Lasinio Model

The phase diagram of cold dense quark matter is studied using the 't Hooft extended Nambu--Jona-Lasinio Model applied to the light quark sector with a finite current mass for the strange quark (up and down are considered in the chiral limit). By relaxing the traditional uniformity assumptions and considering a modulated light quark condensate background we investigate the possible existence of non-uniform phases in this region of the phase diagram. The effects of changes in the coupling strengths of the model are studied and it is shown that the inclusion of flavour mixing combined with the finite current mass of the strange quark catalyses the appearance of the non-uniform phases, extending the domain for their existence.

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