Searcharxiv⌕ Search

arXiv subjects

A. E. Dorokhov

Publications and source records attributed to A. E. Dorokhov.

At least 37 records · Page 2Linked to original sources
arXiv2012

The light-by-light contribution to the muon (g-2) from lightest pseudoscalar and scalar mesons within nonlocal chiral quark model

The light-by-light contribution from the lightest neutral pseudoscalar and scalar mesons to the anomalous magnetic moment of muon is calculated in the framework of the nonlocal SU(3)x SU(3) quark model. The model is based on chirally symmetric four-quark interaction of the Nambu-Jona-Lasinio type and Kobayashi-Maskawa-t`Hooft U_A(1) breaking six-quark interaction. Full kinematic dependence of vertices with off-shell mesons and photons in intermediate states in the light-by-light scattering amplitude is taken into account. The small positive contributions from the scalar mesons stabilize the total result with respect to change of model parameters and reduces to a_μ^{LbL,PS+S}=(6.25\pm 0.83)x10^{-10}.

hep-ph↗
arXiv2011

Bound States in Gauge Theories as the Poincare Group Representations

The bound state generating functional is constructed in gauge theories. This construction is based on the Dirac Hamiltonian approach to gauge theories, the Poincaré group classification of fields and their nonlocal bound states, and the Markov-Yukawa constraint of irreducibility. The generating functional contains additional anomalous creations of pseudoscalar bound states: para-positronium in QED and mesons in QCD in the two gamma processes of the type of γ+ γ= π_0+para-positronium. The functional allows us to establish physically clear and transparent relations between the perturbative QCD to its nonperturbative low energy model by means of normal ordering and the quark and gluon condensates. In the limit of small current quark masses, the Gell-Mann-Oakes-Renner relation is derived from the Schwinger-Dyson (SD) and Bethe-Salpeter (BS) equations. The constituent quark masses can be calculated from a self-consistent non-linear equation.

hep-th↗
arXiv2011

Pseudoscalar meson form factors and decays

In this communication we discuss few topics related with modern experimental data on the physics of light pseudoscalar mesons. It includes the contribution of the pseudoscalar mesons to the muon anomalous magnetic moment (AMM), $g-2$, the rare decays of light pseudoscalar mesons to lepton pair, the transition form factors of pseudoscalar mesons at large momentum transfer, the pion transversity form factor. Measuring the muon anomalous magnetic moment $g-2$ and the rare decays of light pseudoscalar mesons into lepton pair $P\rightarrow l^{+}l^{-} $ serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model predictions the data on the transition form factors of light pseudoscalar mesons play significant role. Recently new data on behavior of these form factors at large momentum transfer was supplied by the BABAR collaboration. Within the nonlocal chiral quark model it shown how to describe these data and how the meson distribution amplitude evolves as a function of the dynamical quark masses and meson masses.

hep-ph↗
arXiv2011

The pseudoscalar hadronic channel contribution of the light-by-light process to the muon (g-2) within the nonlocal chiral quark model

The light-by-light contribution to the anomalous magnetic moment of muon (g-2)_μ from the hadronic exchanges in the neutral pseudoscalar meson channel is calculated in the nonlocal chiral quark model. The full kinematic dependence of the meson-two-photon vertices on the virtualities of the mesons and photons is taken into account. The status of various phenomenological and QCD short-distance constraints is discussed and the comparison with the predictions of other models is performed. It is demonstrated that the effect of the full kinematic dependence in the meson-photon vertices is to reduce the contribution of pseudoscalar exchages to a_μ^{PS,LbL} by approximately factor 1.5 in comparison with the most of previous estimates.

hep-ph↗
arXiv2010

Photon-pion transition form factor: BABAR puzzle is cracked

Recently, the BABAR collaboration published (arXiv:0905.4778) data for the photon-pion transition form factor $F_{πγγ^{\ast}}(Q^{2})$, which are in strong contradiction to the predictions of the standard factorization approach to perturbative QCD. Immediately afterwards, two mechanisms were suggested (A.E. Dorokhov, arXiv:0905.4577; A.V. Radyushkin, arXiv:0906.0323), that logarithmically enhance the form factor asymptotics and therefore provide a qualitatively satisfactory description of the BABAR data. However, the physics of the BABAR effect was not fully clarified. In the present work, based on a nonperturbative approach to the QCD vacuum and on rather universal assumptions, we show that there exists two asymptotic regimes for the pion transition form factor. One regime with asymptotics $F_{πγ^{\ast}γ}(Q^{2})\sim1/Q^{2}$ corresponds to the result of the standard QCD factorization approach, while other violates the standard factorization and leads to asymptotic behavior as $F_{πγ^{\ast}γ}(Q^{2})\sim\ln(Q^{2})Q^{2}$. Furthermore, considering specific nonlocal chiral quark models, we find the region of parameters, where the existing CELLO, CLEO and BABAR data for the pion transition form factor are successfully described.

hep-ph↗
arXiv2010

How the recent BABAR data for P to γγ* affect the Standard Model predictions for the rare decays P to l+l-

Measuring the lepton anomalous magnetic moments $(g-2)$ and the rare decays of light pseudoscalar mesons into lepton pairs $P\to l^{+}l^{-} $, serve as important tests of the Standard Model. To reduce the theoretical uncertainty in the standard model predictions, the data on the charge and transition form factors of the light pseudoscalar mesons play a significant role. Recently, new data on the behavior of the transition form factors $P\toγγ* $ at large momentum transfer were supplied by the BABAR collaboration. There are several problems with the theoretical interpretation of these data: 1) An unexpectedly slow decrease of the pion transition form factor at high momenta, 2) the qualitative difference in the behavior of the pion form factor and the $η$ and $η^\prime$ form factors at high momenta, 3) the inconsistency of the measured ratio of the $η$ and $η^\prime$ form factors with the predicted one. We comment on the influence of the new BABAR data on the rare decay branchings.

hep-ph↗
arXiv2009

Muon g-2, rare decays P \to l^+l^- and transition form factors P \to γγ^*

Measuring the muon anomalous magnetic moment g-2 and the rare decays of light pseudoscalar mesons into lepton pair P \to l+l- serve as important test of the standard model. To reduce the theoretical uncertainty in the standard model predictions the data on the transition form factors of light pseudoscalar mesons play significant role. Recently new data on behavior of these form factors at large momentum transfer was supplied by the BABAR collaboration. We comment on the (in)consistency of these data with perturbative QCD expectation.

hep-ph↗
arXiv2009

Rare decay π^0 \to e^+e^- as a Test of Standard Model

Experimental and theoretical progress concerning the rare decay π^0 \to e^+e^- is briefly reviewed. It includes the latest data from KTeV and a new model independent estimate of the decay branching which show the deviation between experiment and theory at the level of $3.3σ$. The predictions for ηand η' decays into lepton pair are presented. We also comment on the impact on the pion rare decay estimate of the BABAR collaboration on the pion transition form factor at large momentum transfer.

hep-ph↗
arXiv2009

Complete structure dependent analysis of the decay $P \to l^{+}l^{-}$

We use the Mellin-Barnes representation in order to improve the theoretical estimate of mass corrections to the width of light pseudoscalar meson decays into a lepton pair, $P\to l^{+}l^{-}$ . The full resummation of the terms $(M^{2}/Λ^{2}) ^{n},$ $(m^{2}/M^{2}) ^{n}$and $(m^{2}/Λ^{2}) ^{n}$ to the decay amplitude is performed, where $m$ is the lepton mass, $M$ is the meson mass and $Λ\approx m_ρ$ is the characteristic scale of the $P\to γ^{\ast}γ^{\ast}$ form factor. The total effect of mass corrections is quite important for $η(η^{\prime})$ decays. We also comment on the estimation of the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment in the chiral perturbation theory.

hep-ph↗
arXiv2009

Single Spin Asymmetries in High Energy Reactions and Nonperturbative QCD Effects

We discuss some experimental and theoretical results on single spin asymmetries (SSA) in high energy lepton-hadron and hadron-hadron reactions. In particular, recent results on meson SSA obtained by HERMES are considered in detail. We also discuss the SSA results obtained recently by COMPASS, as well as those from BRAHMS, PHENIX and STAR. Special attention is paid to a possible nonperturbative QCD mechanism that might be responsible for the observed meson SSA. This mechanism originates from the spin-flip quark-gluon chromomagnetic interaction induced by the complex topological structure of the QCD vacuum. We argue that in semi-inclusive deep-inelastic scattering a large SSA is expected not only for mesons but also for baryons due to strong nonperturbative final state interactions between $ud$-diquark and $u$-quark in the fragmenting proton.

hep-ph↗
arXiv2008

Recent results on rare decay pi0 to e+e-

Experimental and theoretical progress concerning the rare decay pi0 to e+e- is briefly reviewed. It includes the latest data from KTeV and a new model independent estimate of the decay branching which show the deviation between experiment and theory at the level of 3.3σ.

hep-ph↗
arXiv2008

On mass corrections to the decays P \to l^+l^-

We use the Mellin-Barnes representation in order to improve the theoretical estimate of mass corrections to the width of light pseudoscalar meson decay into a lepton pair, $P\to l^+l^-$ . The full resummation of the terms $\ln(m_l^2/Λ^2)(m_l^2/Λ^2)^n$ and $(m_l^2/Λ^2)^n$ to the decay amplitude is performed, where $m_l$ is the lepton mass and $Λ\approx m_ρ$ is the characteristic scale of the $P\toγ^*γ^*$ form factor. The total effect of mass corrections for the $e^+e^-$ channel is negligible and for the $μ^+μ^-$ channel its order is of a few per cent.

hep-ph↗
arXiv2008

QED radiative corrections to the decay pi^0 to e^+e^-

We reconsider QED radiative corrections (RC) to the $π^{0}\to e^{+}e^{-}$ decay width. One kind of RC investigated earlier has a renormalization group origin and can be associated with the final state interaction of electron and positron. It determines the distribution of lepton pair invariant masses in the whole kinematic region. The other type of RC has a double-logarithmic character and is related to almost on-mass-shell behavior of the lepton form factors. The total effect of RC for the $π^{0}\to e^{+}e^{-}$ decay is estimated to be 3.2% and for the decay $η\to e^{+}e^{-}$ is 4.3%.

hep-ph↗
arXiv2007

Gluon condensate behaviour at filling the Fermi sphere up

The impact of filling up the Fermi sphere with the quarks, which dynamically generated their masses on the instanton liquid at finite temperature and baryonic/quark number density, is investigated. It is demonstrated, in particular, that the boundary of chiral symmetry restoration phase transition is shifted to the larger (about 100 MeV more) value of quark chemical potential compared to the magnitude inherent in the Nambu-Jona-Lasinio model.

hep-ph↗
arXiv2006

Photon distribution amplitudes and light-cone wave functions in chiral quark models

The leading- and higher-twist distribution amplitudes and light-cone wave functions of real and virtual photons are analyzed in chiral quark models. The calculations are performed in the nonlocal quark model based on the instanton picture of QCD vacuum, as well as in the spectral quark model and the Nambu--Jona-Lasinio model with the Pauli-Villars regulator, which both treat interaction of quarks with external fields locally. We find that in all considered models the leading-twist distribution amplitudes of the real photon defined at the quark-model momentum scale are constant or remarkably close to the constant in the $x$ variable, thus are far from the asymptotic limit form. The QCD evolution to higher momentum scales is necessary and we carry it out at the leading order of the perturbative theory for the leading-twist amplitudes. We provide estimates for the magnetic susceptibility of the quark condensate $χ_m$ and the coupling $f_{3γ}$, which in the nonlocal model turn out to be close to the estimates from QCD sum rules. We find the higher-twist distribution amplitudes at the quark model scale and compare them to the Wandzura-Wilczek estimates. In addition, in the spectral model we evaluate the distribution amplitudes and light-cone wave functions of the $ρ$-meson.

hep-ph↗