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D. Ebert

Publications and source records attributed to D. Ebert.

At least 109 records · Page 6Linked to original sources
arXiv1999

Magnetic Oscillations in the Nambu - Jona-Lasinio model

The phase structure of a simple Nambu-Jona-Lasinio model has been investigated at non-zero values of $μ$ and H, where H is an external magnetic field and $μ$ is the chemical potential. On this basis magnetic oscillations effects were considered. It was shown that there are standard (periodic) van Alphen-de Haas magnetic oscillations of some thermodynamical quantities, including magnetization, pressure and particle density in the NJL system. Besides, we have found non-standard, i.e. non-periodic, magnetic oscillations, since the frequency of oscillations is a H-dependent quantity. Finally, there arises an oscillating behaviour not only for thermodynamical quantities, but also for a dynamical quantity like the quark mass. The possibility for magnetic oscillations of some physical quantities inside neutron stars is discussed.

nucl-th↗
arXiv1999

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 v^2/c^2 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.

hep-ph↗
arXiv1999

Heavy quark 1/m_Q contributions in semileptonic B decays to orbitally excited D mesons

Exclusive semileptonic decays of B mesons to orbitally excited D mesons are considered beyond the infinitely heavy quark limit in the framework of the relativistic quark model based on the quasipotential approach. This model agrees with the structure of heavy quark mass corrections predicted by the heavy quark effective theory and allows the determination of corresponding leading and subleading Isgur-Wise functions. It is found that both relativistic and 1/m_Q contributions significantly influence the decay rates. Thus, relativistic transformations of the meson wave functions (Wigner rotation of the light quark spin) already contribute at leading order of the heavy quark expansion and result in a suppression of B\to D^{*}_0eνand B\to D^{*}_1eνdecay rates. On the other hand, the vanishing of the decay matrix elements at zero recoil of a final D^{**} meson in the infinitely heavy quark mass limit makes the 1/m_Q corrections to be very important, and their account results in a substantial enhancement of B\to D_1eνand B\to D^{*}_0eνdecay rates.

hep-ph↗
arXiv1999

Magnetic Oscillations in Dense Cold Quark Matter with Four-Fermion Interactions

The phase structures of Nambu-Jona-Lasinio models with one or two flavours have been investigated at non-zero values of $μ$ and $H$, where $H$ is an external magnetic field and $μ$ is the chemical potential. In the phase portraits of both models there arise infinitely many massless chirally symmetric phases, as well as massive ones with spontaneously broken chiral invariance, reflecting the existence of infinitely many Landau levels. Phase transitions of first and second orders and a lot of tricritical points have been shown to exist in phase diagrams. In the massless case, such a phase structure leads unavoidably to the standard van Alphen-de Haas magnetic oscillations of some thermodynamical quantities, including magnetization, pressure and particle density. In the massive case we have found an oscillating behaviour not only for thermodynamical quantities, but also for a dynamical quantity as the quark mass. Besides, in this case we have non-standard, i.e. non-periodic, magnetic oscillations, since the frequency of oscillations is an $H$-dependent quantity.

hep-ph↗
arXiv1998

Decays of excited strange mesons in the extended NJL model

A chiral U(3)xU(3) 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. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the kaon, K^* and ϕare described with the help of two form factors. The values for the decay widths of the processes K^*' --> ρK, K^*' --> K^* π, K^*'--> K π, ϕ' --> K^* K, ϕ' --> KK, K' --> K ρ, K' --> K^* πand K' --> K 2πare obtained in qualitative agreement with the experimental data.

hep-ph↗
arXiv1998

Relativistic properties of the quark-antiquark potential

The relativistic transformation properties of the heavy quark-antiquark interaction potential are considered in the framework of the relativistic quark model. A special attention is paid to the long-range (confining) contribution to the spin-independent part of qq bar interaction. The retardation effects are consistently taken into account.

hep-ph↗
arXiv1998

Mass spectrum of orbitally and radially excited heavy-light mesons in the relativistic quark model

The mass spectrum of orbitally and radially excited states of B and D mesons is calculated in the framework of the relativistic quark model. The expansion in inverse powers of the heavy quark mass is carried out up to the first order, while the light quark is treated without expansion. We find that the relativistic treatment of the light quark plays an important role. Different patterns of P level inversion are discussed. The obtained masses of orbitally and radially excited states are in accord with available experimental data and heavy quark symmetry relations.

hep-ph↗
arXiv1998

Exclusive semileptonic decays of B mesons to orbitally excited D mesons in the relativistic quark model

Exclusive semileptonic B meson decays to orbitally excited D mesons are investigated in the infinitely heavy quark limit in the framework of the relativistic quark model based on the quasipotential approach. The B\to D^{**}eνIsgur-Wise functions τ_{3/2}(w) and τ_{1/2}(w) are determined. It is found that the relativistic transformation of the meson wave functions (Wigner rotation of the light quark spin) contribute already at the leading order of the heavy quark expansion.

hep-ph↗
arXiv1997

Generation of a QCD-induced Chern-Simons like term in QED

A possibility is discussed that new nontrivial Chern-Simons like terms may be generated in (3+1)--dimensional QED Lagrangian, when induced by quark loops interacting with a non-abelian background field in an SU(2) model of QCD.

hep-th↗
arXiv1997

Modelling the QCD Phase Transition with an Effective Lagrangian of Light and Massive Hadrons

The temperature dependence of quark and gluon condensates in QCD as precursor of the chiral and deconfining phase transition is modelled with a conformally extended non-linear sigma-model including broken chiral and scale invariance. The model is further enlarged by including (free) heavier hadrons. Within this frame we then study the interplay of QCD scale breaking effects and heavier hadrons in chiral symmetry restoration.

hep-ph↗
arXiv1997

Bosonization in Particle Physics

Path integral techniques in collective fields are shown to be a useful analytical tool to reformulate a field theory defined in terms of microscopic quark (gluon) degrees of freedom as an effective theory of collective boson (meson) fields. For illustrations, the path integral bosonization approach is applied to derive a (non)linear sigma model from a Nambu-Jona-Lasinio (NJL) quark model. The method can be extended to include higher order derivative terms in meson fields or heavy-quark symmetries. It is also approximately applicable to QCD.

hep-ph↗
arXiv1997

Hadronization in Particle Physics

The method of path integral hadronization is applied to a local quark-diquark toy model in order to derive an effective chiral meson-baryon Lagrangian. Further generalizations to models including both scalar and axial-vector diquarks as well as nonlocal interactions are discussed.

hep-ph↗
arXiv1997

Curvature Expansion for the Gluodynamics String including Perturbative Gluonic Contributions

Perturbation theory in the nonperturbative QCD vacuum and the non-Abelian Stokes theorem, representing a Wilson loop in the SU(2) gluodynamics as an integral over all the orientations in colour space, are applied to a derivation of the correction to the string effective action in the lowest order in the coupling constant $g$. This correction is due to the interaction of perturbative gluons with the string world sheet and affects only the coupling constant of the rigidity term, while its contribution to the string tension of the Nambu-Goto term vanishes. The obtained correction to the rigidity coupling constant multiplicatively depends on the colour "spin" of the representation of the Wilson loop under consideration and a certain path integral, which includes the background Wilson loop average.

hep-th↗
arXiv1997

Faddeev equation for heavy baryons in the quark-diquark picture

We describe heavy baryons as bound states of a quark and a diquark. For this purpose we derive the Faddeev equation for baryons containing a single heavy quark from a Nambu-Jona-Lasinio type of model which is appropriately extended to include also heavy quarks. The latter are treated in the heavy mass limit. The heavy baryon Faddeev equation is then solved using a static approximation for the exchanged quark.

hep-ph↗