arXiv subjects

D. Ebert

Publications and source records attributed to D. Ebert.

124 records · Page 7Linked to original sources

arXiv1997

Excited pions, rho- and omega-mesons and their decays in a chiral SU(2) x SU(2) Lagrangian

A chiral SU(2) x 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 quark model with separable non-local interactions, with form factors corresponding to 3-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, rho-and omega-mesons are described with the help of two form factors. The weak decay constant F_pi' is calculated. The values for the decay widths of the processes rho -> 2 pi, pi' -> rho pi, rho' -> 2 pi, rho' -> omega pi and omega' -> rho pi are obtained in agreement with the experimental data.

hep-ph↗

arXiv1997

Dimensional structural constants from chiral and conformal bosonization of QCD

We derive the dimensional non-perturbative part of the QCD effective action for scalar and pseudoscalar meson fields by means of chiral and conformal bosonization. The related structural coupling constants L_5 and L_8 of the chiral lagrangian are estimated using general relations which are valid in a variety of chiral bosonization models without explicit reference to model parameters. The asymptotics for large scalar fields in QCD is elaborated, and model-independent constraints on dimensional coupling constants of the effective meson lagrangian are evaluated. We determine also the interaction between scalar quarkonium and the gluon density and obtain the scalar glueball-quarkonium potential.

hep-ph↗

arXiv1997

Chiral phase transitions in strong chromomagnetic fields at finite temperature and dimensional reduction

Dynamical fermion mass generation in external chromomagnetic fields is considered at non--zero temperature. The general features of dynamical chiral symmetry breaking ($DχSB$) are investigated for several field configurations in relation to their symmetry properties and the form of the quark spectrum. According to the fields, there arises dimensional reduction by one or two units. In all cases there exists $DχSB$ even at weak quark attraction, confirming the idea about the dimensional insensitivity of this mechanism in a chromomagnetic field.

hep-ph↗

arXiv1997

Exclusive nonleptonic decays of B mesons

The energetic exclusive two-body nonleptonic decays of B mesons are investigated in the framework of the relativistic quark model within the factorization approximation. The heavy quark expansion is used for the calculation of form factors. The obtained results are in agrement with available experimental data.

hep-ph↗

arXiv1996

An action of the gluodynamics string from the Wilson loop expansion

The nonabelian Stokes theorem, representing a Wilson loop as an integral over all the orientations in colour space, and the cumulant expansion are used for derivation of the string effective action in SU(2) gluodynamics. The obtained theory is the theory of the rigid string interacting with the rank two antisymmetric Kalb-Ramond fields. In this model there exists a phase where there are no problems of crumpling and wrong high temperature behaviour of the string tension, which are present in the free rigid string theory. The Langevin approach to stochastic quantization of the obtained theory is applied.

hep-th↗

arXiv1996

Extended NJL Model for light and heavy mesons without q-qbar thresholds

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-qbar 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 satisfactoring 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.

hep-ph↗

arXiv1996

Heavy baryons in the relativistic quark model

In the framework of the relativistic quasipotential quark model the mass spectrum of baryons with two heavy quarks is calculated. The quasipotentials for interactions of two quarks and of a quark with a scalar and axial vector diquark are evaluated. The bound state masses of baryons with $J^P=\frac{1}{2}^+, \frac{3}{2}^+$ are computed.

hep-ph↗

arXiv1996

Curvature expansion for the background-induced gluodynamics string

Using cumulant expansion for an averaged Wilson loop we derive an action of the gluodynamics string in the form of a series in powers of the correlation length of the vacuum. In the lowest orders it contains the Nambu-Goto term and the rigidity term with the coupling constants computed from the bilocal correlator of gluonic fields. Some higher derivative corrections are calculated.

hep-th↗

arXiv1996

Kaon polarizability in the Nambu-Jona-Lasinio model at zero and finite temperature

Using recent data for the decays $f_0 \to γγ$, $f_0 \to ππ$, we determine the mixing angle of scalar mesons in a chiral quark $σ$-model. This value is employed to analyze of the kaon polarizability. It is shown that pole diagrams from intermediate scalar mesons and their mixing angle significantly affect the electromagnetic polarizability of charged and neutral kaons. Our results are compared with other models and the results of the chiral symmetry limit. The temperature dependence of the kaon polarizabilities is investigated.

hep-ph↗

arXiv1996

Heavy Hadron Spectrum and Interactions

Starting from the approximate symmetries of QCD, namely chiral symmetry for light quarks and spin and flavor symmetry for heavy quarks, we investigate the low-energy properties of heavy hadrons. For this purpose we construct a consistent picture of quark-antiquark and quark-diquark interactions as a low-energy approximation to the flavor dynamics in heavy mesons and heavy baryons, respectively. Using standard functional integration tools, we derive an effective Lagrangian in terms of heavy hadron fields and discuss several properties, like the mass spectrum, coupling and decay constants, Isgur-Wise form factors.

hep-ph↗

arXiv1995

A diquark model for baryons containing one heavy quark

We present a phenomenological ansatz for coupling a heavy quark with two light quarks to form a heavy baryon. The heavy quark is treated in the heavy mass limit, and the light quark dynamics is approximated by propagating scalar and axial vector 'diquarks'. The resulting effective lagrangian, which incorporates heavy quark and chiral symmetry, describes interactions of heavy baryons with Goldstone bosons in the low energy region. As an application, the Isgur--Wise form factors are estimated.

hep-ph↗

arXiv1994

To the problem of 1/Nc approximation in the Nambu-Jona-Lasinio model

In this article, the gap equation for the constituent quark mass in the U(2)*U(2) Nambu-Jona-Lasinio model for the 1/Nc approximation is investigated. It is shown that taking into account scalar isovector mesons plays an important role for the correct description of quark masses in this approximation. The role of the Ward identity in calculations of 1/Nc corrections to the meson vertex functions is shortly discussed.

hep-th↗

arXiv1994

The $(0^+,1^+)$ heavy meson multiplet in an extended NJL model

In this letter we reconsider the previously given description of heavy mesons within a bosonized extended NJL model that combines heavy quark and chiral symmetry. In that work the naive gradient expansion of the quark determinant was used, which satisfactorily works in the light sector but does not adequately describe the heavy $(0^+,1^+)$ mesons. By investigating the exact momentum dependence of the quark loop we demonstrate that the naive gradient expansion in the heavy sector is not the right method to treat the unphysical $q\bar{q}$--thresholds which would be absent in confining theories. We propose a modified gradient expansion which adequately extrapolates from the low--momentum region beyond threshold. This expansion gives a satisfactory description even of the $(0^+,1^+)$ heavy mesons whose masses are significantly above threshold.

hep-ph↗

arXiv1994

Effective Meson Lagrangian with Chiral and Heavy Quark Symmetries from Quark Flavor Dynamics

By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy $B$ and $D$ mesons with pseudoscalar Goldstone bosons and light vector and axial--vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur--Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit $SU(3)_F$ symmetry breaking effects are estimated and, if possible, confronted with experiment.

hep-ph↗

arXiv1993

On the Origin of the Enhancementof CP-violating Charge Asymmetries in $K \rightarrow 3π$ Decays Predicted from Chiral Theory

We present an analysis of the enhancement of CP-violating charge asymmetries in $K \rightarrow 3π$ decays. Calculations of decay amplitudes are performed on the basis of bosonized strong and weak Lagrangians derived from QCD-motivated quark Lagrangians. We show that the interplay of fourth-order contributions of chiral Lagrangians for strong interactions and penguin operators in weak interactions significantly enhances the charge asymmetries.

hep-ph↗

arXiv1993

Heat-Kernel Calculation of Quark Determinant and Computer Algebra

In this paper there we describe the calculational background of deriving a strong meson Lagrangian from the Nambu--Jona-Lasinio quark model using the computer algebra systems FORM and REDUCE in recursive algorithms, based on the heat-kernel method for the calculation of the quark determinant.

hep-ph↗