arXiv subjects

K. Goeke

Publications and source records attributed to K. Goeke.

101 records · Page 6Linked to original sources

arXiv1994

Electromagnetic Nucleon Properties and Quark Sea Polarization

In this paper we present the derivation as well as the numerical results for all electromagnetic form factors of the nucleon within the chiral quark soliton model in the semiclassical quantization scheme. The model is based on a semibosonized Nambu -- Jona-Lasinio lagrangean where the boson fields are treated as classical ones. Other observables, namely the nucleon mean squared radii, the magnetic moments and the nucleon--$Δ$ splitting are calculated as well. The calculations have been done taking into account the quark sea polarization effects. The final results, including rotational $1/N_c$ corrections, are compared with the existing experimental data and they are found to be in a good agreement for the constituent quark mass of $400-420$ MeV.

hep-ph↗

arXiv1994

Axial Properties of the Nucleon with $1/N_c$-Corrections in the solitonic SU(3)-NJL-Model

Within the semibosonized SU(3)-NJL model the mass splittings of baryons and the axial vector coupling constants of the nucleon are evaluated. The mass splittings of the hyperons are reproduced with great accuracy if second order corrections in $m_s$ are taken into account. New corrections to the axial vector currents coming from the subleading terms in the $1/N_c$ expansion are shown to be non-vanishing and substantially improving the phenomenological predictions for axial quantities. Finally the numerical values for the $g_{\rm A}$'s are $g_A^{(0)}=0.37$, $g_A^{(3)}=1.38$ and $g_A^{(8)}=0.31$ reproducing reasonably well the recent data from lepton scattering.

hep-ph↗

arXiv1994

Baryons in Effective Chiral Quark Models with Polarized Dirac Sea

We give a comprehensive review of concepts and numerical calculations for SU(2) and SU(3) baryonic systems which are considered as many body systems composed of three quarks coupled to a polarized Dirac sea by a Nambu--Jona-Lasinio like interaction. The general formalism as well as the construction and numerical solution of non-topological mean field solitons are exhibited. Systems with good spin/flavour/isospin/momentum quantum numbers are obtained by using the SU(2)/SU(3)-cranking and the pushing approach. The article contains also recent results for various extensions of the model, e.g. vector and axialvector couplings or the inclusion of scale invariance. Furthermore the relationship of this approach to topological models (Skyrme type) as well as to (valence-)quark-meson models (Gell-Mann--Levi chiral sigma model) is explained. (to be publ. in Rep.Prog.Phys.)

hep-ph↗

arXiv1993

Electromagnetic nucleon properties and quark sea polarization in the Nambu-Jona-Lasinio model

In this paper we present the derivation as well as the numerical results for all electromagnetic form factors of the nucleon within the semibosonized Nambu--Jona-Lasinio (chiral quark soliton) model. Other observables, namely the nucleon mean squared radii, the magnetic moments and the nucleon--$Δ$ splitting are also computed. The calculation has been done taking into account the quark sea polarization effects. The final results, including rotational $1/N_c$ corrections, are compared with the existent experimental data and they are found to be in a good agreement for the constituent quark mass of $400$--$420\ MeV$.

hep-ph↗

arXiv1993

$1/N_c$ Rotational Corrections to $g_A$ and Isovector Magnetic Moment of the Nucleon

The $1/N_c$ rotational corrections to the axial vector constant and the isovector magnetic moment of the nucleon are studied in the Nambu -- Jona-Lasinio model. We follow a semiclassical quantization procedure in terms of path integrals in which we can include perturbatively corrections in powers of angular velocity $Ω\sim \frac 1{N_c}$. We find non-zero $1/N_c$ order corrections from both the valence and the Dirac sea quarks. These corrections are large enough to resolve the long-standing problem of a strong underestimation of both $g_A$ and $μ^{IV}$ in the leading order. The axial constant $g_A$ is well reproduced, whereas the isovector magnetic moment $μ^{IV}$ is still underestimated by 25 \%.

hep-ph↗

arXiv1993

Electric Polarizability of the Nucleon in the Nambu--Jona-Lasinio Model

The electric polarizability of the nucleon is calculated in the soliton approach to the Nambu--Jona-Lasinio model. We analyze the leading-$N_c$ contributions, as well as the effects of rotational $1/N_c$ corrections and $Δ$-$N$ mass splitting. Our model prediction is substantially reduced compared to other soliton calculations, and is closer to the experimental value.

hep-ph↗

arXiv1993

On Size and Shape of the Average Meson Fields in the Semibosonized Nambu & Jona-Lasinio Model

We consider a two-flavor Nambu \& Jona-Lasinio model in Hartree approximation involving scalar-isoscalar and pseudoscalar-isovector quark-quark interactions. Average meson fields are defined by minimizing the effective Euklidean action. The fermionic part of the action, which contains the full Dirac sea, is regularized within Schwinger's proper-time scheme. The meson fields are restricted to the chiral circle and to hedgehog configurations. The only parameter of the model is the constituent quark mass $M$ which simultaneously controls the regularization. We evaluate meson and quark fields self-consistently in dependence on the constituent quark mass. It is shown that the self-consistent fields do practically not depend on the constituent quark mass. This allows us to define a properly parameterized reference field which for physically relevant constituent masses can be used as a good approximation to the exactly calculated one. The reference field is chosen to have correct behaviour for small and large radii. To test the agreement between self-consistent and reference fields we calculate several observables like nucleon energy, mean square radius, axial-vector constant and delta-nucleon mass splitting in dependence on the constituent quark mass. The agreement is found to be very well. Figures available on request.

nucl-th↗

arXiv1993

Rotational Corrections to Axial Currents in Semibosonized SU(3) Nambu--Jona-Lasinio Model

We examine $O(1/\Ne)$ rotational corrections to axial couplings \gt~ and \go~ in the framework of the semibosonized SU(3) Nambu--Jona-Lasinio model. A novelty is due to the observation that the rotational (cranking) velocity and the rotation matrix itself do not commute within semiclassical quantization scheme. If time ordering in the quark loop is maintained new contributions, which have no analogue in the Skyrme model, appear. They substantially improve numerical results for the axial couplings which without the present corrections are badly underestimated.

hep-ph↗

arXiv1993

Hyperons as Solitons in Chiral Quark Model

The paper describes the quantization of the SU(3) smibosonized Nambu-Jona-Lasinio model and results for mass splittings, including isospin splittings, and axial couplings. The agreement with the data is surprisingly good.

hep-ph↗

arXiv1993

B=1 Soliton of the Nambu - Jona-Lasinio model in medium}

The solitonic sector of the Nambu - Jona-Lasinio model with baryon number one is solved in the presence of an external medium. The calculations fully include the polarization of both the Dirac sea and the medium as well as the Pauli blocking effect. We found that with an increasing density the medium destabilizes the soliton. At finite medium density the soliton mass gets reduced whereas the mean square baryon radius shows an increase - a swelling of the soliton. At some critical density of about two times nuclear matter density there is no localized solution - the soliton disappears.

hep-ph↗

arXiv1993

Nucleon Properties and Restoration of Chiral Symmetry at Finite\nl Density and Temperature in an Effective Theory

Modifications of baryon properties due to the restoration of the chiral symmetry in an external hot and dense baryon medium are investigated in an effective chiral quark-meson theory. The nucleon arises as a soliton of the Gell-Mann - Lévi $\zs$-model, the parameters of which are chosen to be the medium-modified meson values evaluated within the Nambu - Jona-Lasinio model. The nucleon properties are obtained by means of variational projection techniques. The nucleon form factors as well as the nucleon delta transition form factors are evaluated for various densities and temperatures of the medium. Similar to the chiral phase transition line the critical curve in the $T-\zr$ plane for delocalization of the nucleon is non-monotonic and this feature is reflected in all nucleon properties. At medium densities of about $(2-3) \rnm$ the baryonic phase exists only at intermediate temperatures. For finite temperature and densities the nucleon form factors get strongly reduced at finite transfer momenta.

hep-ph↗