arXiv subjects

A. V. Nefediev

Publications and source records attributed to A. V. Nefediev.

At least 91 records · Page 5Linked to original sources

arXiv2002

Collision damping in the pi 3He -> d'N reaction near the threshold

We present a simple quantum mechanical model exploiting the optical potential approach for the description of collision damping in the reaction pi 3He -> d'N near the threshold, which recently has been measured at TRIUMF. The influence of the open d'N -> NNN channel is taken into account. It leads to a suppression factor of about ten in the d' survival probability. Applications of the method to other reactions are outlined.

nucl-th↗

arXiv2002

Orbitally excited D and B mesons in the approach of the QCD string with quarks at the ends

In this letter we discuss the masses and the splittings of 1(2S+1)P_J states in the spectrum of D and B mesons, as they appear in the approach of the QCD string with quarks at the ends. We find good agreement of our predictions with those of other QCD-motivated models as well as with the lattice and experimental data, including recent experimental results. We discuss the ordering pattern for P levels in D- and B-mesonic spectrum.

hep-ph↗

arXiv2002

Vacuum replicas in QCD

The properties of the vacuum are addressed in the two- and four-dimensional quark models for QCD. It is demonstrated that the two-dimensional QCD ('t Hooft model) possesses only one possible vacuum state - the solution to the mass-gap equation, which provides spontaneous breaking of the chiral symmetry (SBCS). On the contrary, the four-dimensional theory with confinement modeled by the linear potential supplied by the Coulomb OGE interaction, not only has the chirally-noninvariant ground vacuum state, but it possesses an excited vacuum replica, which also exhibits SBCS and can realize as a metastable intermediate state of hadronic systems. We discuss the influence of the latter on physical observables as well as on the possibility to probe the vacuum background fields in QCD.

hep-ph↗

arXiv2001

Two-dimensional QCD in the Coulomb gauge

In the present paper we discuss various aspects of the 't Hooft model for two-dimensional QCD in the limit of infinite number of colours in the Coulomb gauge. The properties of mesonic excitations are addressed, with special attention paid to the pionic one. The twofold role of the pion is discussed: being a genuine quark-antiquark state it is also a Goldstone boson of two-dimensional QCD. In particular, it is demonstrated explicitly how the soft-pion theorems are satisfied. It is pointed out that the Coulomb-gauge choice seems to be indispensable in studies of hadronic observables with the pions involved.

hep-ph↗

arXiv2001

QCD_2 in the axial gauge revisited

The 't Hooft model for the two-dimensional QCD in the limit of infinite number of colours is studied in the axial gauge. The mass-gap and the bound-state equations are derived using the two consequent Bogoliubov-like transformations. Chiral properties of the model are studied in the Hamiltonian and matrix approaches to the latter. Special attention is payed to the explicit pionic solution of the bound-state equation.

hep-ph↗

arXiv2001

Light-light and heavy-light mesons in the model of QCD string with quarks at the ends

The variational einbein field method is applied to the model of the QCD string with quarks at the ends for the case of light-light and heavy-light mesons. Special attention is payed to the proper string dynamics. The correct string slope of the Regge trajectories is reproduced for light-light states which comes out from the picture of rotating string. Masses of several low-lying orbitally and radially excited states in the D, D_s, B, and B_s meson spectra are calculated and a good agreement with the experimental data as well as with recent lattice calculations is found. The role of the string correction to the interquark interaction is discussed at the example of the identification of D*'(2637) state recently claimed by DELPHI Collaboration. For the heavy-light mesons the standard constants used in Heavy Quark Effective Theory are extracted and compared to the results of other approaches.

hep-ph↗

arXiv2001

QCD string in light-light and heavy-light mesons

The spectra of light-light and heavy-light mesons are calculated within the framework of the QCD string model, which is derived from QCD in the Wilson loop approach. Special attention is payed to the proper string dynamics that allows us to reproduce the straight-line Regge trajectories with the inverse slope being 2πσfor light-light and twice as small for heavy-light mesons. We use the model of the rotating QCD string with quarks at the ends to calculate the masses of several light-light mesons lying on the lowest Regge trajectories and compare them with the experimental data as well as with the predictions of other models. The masses of several low-lying orbitally and radially excited heavy--light states in the D, D_s, B, and B_s meson spectra are calculated in the einbein (auxiliary) field approach, which has proven to be rather accurate in various calculations for relativistic systems. The results for the spectra are compared with the experimental and recent lattice data. It is demonstrated that an account of the proper string dynamics encoded in the so-called string correction to the interquark interaction leads to an extra negative contribution to the masses of orbitally excited states that resolves the problem of the identification of the D(2637) state recently claimed by the DELPHI Collaboration. For the heavy-light system we extract the constants \barΛ, λ_1, and λ_2 used in Heavy Quark Effective Theory (HQET) and find good agreement with the results of other approaches.

hep-ph↗

arXiv2001

Heavy-light mesons spectrum from the nonperturbative QCD in the einbein field formalism

The spectrum of B and D mesons (including the low lying orbitally and radially excited states) is calculated using the quark-antiquark Hamiltonian derived from QCD in the einbein field formalism. Spin-spin and spin-orbit terms due to the confinement and OGE interactions are taken into account as perturbations. Results for the masses and splittings are confronted to the experimental and recent lattice data and are demonstrated to be in a reasonable agreement with both. We find that the orbital excitations with l=2 and l=3 for D meson lie approximately in the same region as its first radial excitation that might solve the mystery of the extremely narrow D(2637) state recently claimed by DELPHI Collaboration.

hep-ph↗

arXiv2000

Light-light and heavy-light mesons spectra from nonperturbative QCD

Properties of light-light mesons are described by the effective Hamiltonian with spinless quarks derived from QCD. The spectrum is computed by the WKB method and shown to reproduce the celebrated linear Regge trajectories even for the lowest levels. The correct string slope of the trajectories naturally appears in the present approach as the string dynamics is taken into account properly. Similar method is applied to heavy-light mesons and a set of corrections to the Hamiltonian is taken into account including spin-spin and Tomas spin-orbit interactions. The numerical results for the spectrum are compared with the experimental data and with the results of recent lattice calculations.

hep-ph↗

arXiv2000

Strong hadronic decays in QCD_2

Strong hadronic decays are discussed in the 't Hooft model for the two-dimensional QCD in the limit of infinite number of colours. Adler selfconsistency condition is derived for decays with pions in the final state and the corresponding amplitude is demonstrated to vanish identically in the chiral limit.

hep-ph↗

arXiv2000

Strong decays and Adler selfconsistency condition in two-dimensional QCD

Strong mesonic decays are studied in the framework of the 't Hooft model for the two-dimensional QCD in the axial gauge. Special attention is payed to the processes with pions in the final state involved and the low energy theorems have been checked including the "Adler zero". It is demonstrated explicitly that in the chiral limit any three-meson decay amplitude with at least one pion vertex vanishes identically for any values of the external momenta. Ward identities for the dressed vector and axial-vector currents vertices are identified and their relationship to the pionic vertex are discussed.

hep-ph↗

arXiv1999

Hamiltonian approach to QCD_2 in the axial gauge

The Hamiltonian approach is developed for QCD_2 in the limit of infinite number of colours N_C ('t Hooft model). Bosonization of the theory is performed explicitly and the generalized Bogoliubov transformation for the composite boson operators is introduced and used to bring the Hamiltonian into diagonal form in the two-body sector. The resulting theory is re-formulated in terms of effective degrees of freedom and describes the free mesons with creation and annihilation operators commuting in the canonical way. Corrections in N_C to the leading term in the Hamiltonian describe the interaction between mesons and can be used to consider their decays. Chiral properties of the theory are discussed and it is shown that the backward motion of the chiral pion (Goldstone mode) is not suppressed and should contribute to the decays amplitudes.

hep-ph↗

arXiv1999

Hamiltonian approach to the bound state problem in QCD_2

Bosonization of the two-dimensional QCD in the large N_C limit is performed in the framework of Hamiltonian approach in the Coulomb gauge. The generalized Bogoliubov transformation is applied to diagonalize the Hamiltonian in the bosonic sector of the theory, and the composite operators creating/annihilating bosons are obtained in terms of dressed quark operators. The bound state equation is reconstructed as a result of the generalized Bogoliubov transformation, and the form of its massless solution, chiral pion, is found explicitly. Chiral properties of the theory are discussed.

hep-ph↗

arXiv1999

Rotating QCD string and the meson spectrum

The spectra of light-light and heavy-light mesons are described by spinless Salpeter equation and Dirac equation respectively, which predict linear dependence of the meson mass squared M^2 on angular momentum J and number of radial nodes n. Both spectra are computed by the WKB method and shown to agree with exact numerical data within few percent even for the lowest levels. The drawback of Salpeter and Dirac equation is that (inverse) Regge slopes do not coincide with the string ones, 2πσand πσrespectively, because the string dynamics is not taken into account properly. The lacking string rotation is introduced via effective Hamiltonian derived from QCD which generates linear Regge trajectories for light mesons with the correct string slope.

hep-ph↗

arXiv1998

Quantum mechanics of confinement and chiral symmetry breaking in two-dimensional QCD

The system of light quark and heavy anti-quark source is studied in 1+1 QCD in the large $N_C$ limit. Making use of the modified Fock-Schwinger gauge allows to consider simultaneously the spectroscopical problem of the q\bar Q bound states and the problem of the light quark Green function. The Dirac-type equation for the spectrum of the system is proved to be equivalent to the well-known 't Hooft one in the one body limit. The unitary transformation from the Dirac-Pauli representation to the Foldy-Wouthuysen one is carried out explicitly, and it is shown that the equation in the Foldy-Wouthuysen representation can be treated as a gap equation which defines the light quark self-energy in the modified Fock-Schwinger gauge. The Foldy--Wouthuysen angle is found to play the role of the Bogoliubov-Valatin one and to give the standard value of the chiral condensate. Connections of the given formalism to the standard four-dimensional QCD are outlined and discussed.

hep-ph↗

arXiv1997

Classical antiparticles, quantum supersymmetry anomaly and constituent models

The two ways of constrained systems quantization are considered from the point of view of their self-consistency at the quantum level. With a transparent example of a particle in the external electromagnetic field we demonstrate that the procedure of gauge fixing turns out rather dangerous and may lead to a quantum anomaly in the operator algebra. We discuss additional classical symmetries as an essential element for tracing out this anomaly. The two cases of a spinning and a spinless particles in the external electromagnetic field are discussed to illustrate the situation.

hep-ph↗

arXiv1997

QCD_2 in the modified Fock-Schwinger gauge

The system of light quark and heavy antiquark source is studied in 1+1 QCD in the large N_C limit. The situation is demonstrated to be the two dimensional analogue of the problem in 3+1 QCD corresponding to the essentially nonlocal case of zero vacuum correlation length, which does not allow perturbative treatment. The modified Fock-Schwinger gauge condition is employed to derive the effective Dirac-type equation for the spectrum, which is proved to be equivalent to the 't Hooft equation in the limit of one heavy mass. The chiral condensate is shown to appear naturally in the given approach and to coincide with the convenient value.

hep-ph↗

arXiv1997

Straight-line string in the einbein field formalism

The canonical description of the straight-line string is given in the einbein field formalism. The system is quantized and Regge spectrum is reproduced. The covariant analogue of the Newton-Wigner coordinate is found, and peculiarities of the gauge fixing in τ-reparametrization group are discussed.

hep-ph↗