D. Ebert

Extended NJL model for light and heavy mesons without q-q thresholds

Abstract We consider the NJL model as an effective quark theory to describe the interaction which is responsible for the quark flavor dynamics at intermediate energies. In addition to the usual ultraviolet cut-off which is necessary since the model is non-renormalizable, we also introduce an infrared cut-off which drops off the unknown confinement part of the quark interaction, which is believed to be less important for the flavor dynamics. The infrared cut-off eliminates all q- q thresholds, which plague the application of the usual NJL model beyond low-energy pion physics. We apply this two-cut-off prescription to the extended NJL model with chiral and heavy quark symmetries proposed recently by us. We find a satisfactorily description even of the heavy mesons with spin/parity J p = (0 + , 1 + ). Furthermore, the shape-parameters of the Isgur-Wise function are studied as a function of the residual heavy meson mass.

Absence of gravitational contributions to the running Yang-Mills coupling

Abstract The question of a modification of the running gauge coupling of (non-)Abelian gauge theories by an incorporation of the quantum gravity contribution has recently attracted considerable interest. In this Letter we perform an involved diagrammatical calculation in the full Einstein–Yang–Mills system both in cut-off and dimensional regularization at one-loop order. It is found that all gravitational quadratic divergencies cancel in cut-off regularization and are trivially absent in dimensional regularization so that there is no alteration to asymptotic freedom at high energies. This settles the previously open question of a potential regularization scheme dependence of the one-loop β function traditionally computed in the background field approach. Furthermore we show that the remaining logarithmic divergencies give rise to an extended effective Einstein–Yang–Mills Lagrangian with a counterterm of dimension six.

Quark-antiquark potential with retardation and radiative contributions and the heavy quarkonium mass spectra

The charmonium and bottomonium mass spectra are calculated with the systematic account of all relativistic corrections of order

EXCITED PIONS, ρ- AND ω-MESONS AND THEIR DECAYS IN A CHIRAL SU(2) × SU(2) LAGRANGIAN

{v}^{2}{/c}^{2}

Quark droplets stability induced by external magnetic field

and the one-loop radiative corrections. Special attention is paid to the contribution of the retardation effects to the spin-independent part of the quark-antiquark potential, and a general approach to accounting for retardation effects in the long-range (confining) part of the potential is presented. A good fit to available experimental data on the mass spectra is obtained.

String representation of field correlators in the Dual Abelian Higgs Model

A chiral SU(2) × SU(2) Lagrangian containing, besides the usual meson fields, their first radial excitations is considered. The Lagrangian is derived by bosonization of the Nambu–Jona-Lasinio (NJL) quark model with separable nonlocal interactions, with form factors corresponding to three-dimensional ground and excited state wave functions. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the pions, ρ-and ω-mesons are described with the help of two form factors. The weak decay constant Fπ′ is calculated. The values for the decay widths of the processes ρ→2π, π′→ρπ, ρ′→2π, ρ′→ωπ and ω′→ρπ are obtained in agreement with the experimental data.

Radiative M1-decays of heavy-light mesons in the relativistic quark model

Abstract The influence of a constant homogeneous external magnetic field H on the formation and stability of quark droplets is investigated within a simple Nambu–Jona-Lasinio model by using a thermodynamic approach. For a vanishing magnetic field stable quark droplets, which are schematically the bags of massless quarks, are allowed to exist only at G > G bag , where G is the quark coupling constant, G bag =1.37 G crit , and G crit is the value of the coupling constant above which chiral symmetry is spontaneously broken down. On the other hand, a nonvanishing external magnetic field can induce the stability of quark droplets so that they may exist even at G G bag . In this case, depending on the value of H , quark droplets are composed either of massive or massless quarks.

String representation of field correlators in the SU(3) gluodynamics

Abstract. By making use of the path integral duality transformation, we derive the string representation for the partition function of an extended Dual Abelian Higgs Model containing gauge fields of external currents of electrically charged particles. By the same method, we obtain the corresponding representations for the generating functionals of gauge field and monopole current correlators. In the case of bilocal correlators, the obtained results are found to be in agreement with the dual Meissner scenario of confinement and the Stochastic Model of the QCD vacuum.

MODELLING THE QCD PHASE TRANSITION WITH AN EFFECTIVE LAGRANGIAN OF LIGHT AND MASSIVE HADRONS

Abstract Radiative magnetic dipole decays of heavy–light vector mesons into pseudoscalar mesons V → Pγ are considered within the relativistic quark model. The light quark is treated completely relativistically, while for the heavy quark the 1/ m Q expansion is used. It is found that relativistic effects result in a significant reduction of decay rates. Comparison with previous predictions and recent experimental data is presented.

Effective string action for the U(1)×U(1) dual Ginzburg–Landau theory beyond the London limit

Abstract The string representation of the Abelian projected SU(3)-gluodynamics partition function is derived by using the path-integral duality transformation. On this basis, we also derive analogous representations for the generating functionals of correlators of gluonic field strength tensors and monopole currents, which are finally applied to the evaluation of the corresponding bilocal correlators. The large distance asymptotic behaviours of the latter turn out to be in a good agreement with existing lattice data and the Stochastic Model of the QCD vacuum.