arXiv subjects

W. Bentz

Publications and source records attributed to W. Bentz.

28 records · Page 2Linked to original sources

arXiv2005

The generalized parton distributions of the nucleon in the NJL model based on the Faddeev approach

We study the generalized parton distributions, including the helicity-flip ones, using Nambu-Jona-Lasinio model based on a relativistic Faddeev approach with `static approximation'. Sum rules relating the generalized parton distributions to nucleon electromagnetic form factors are satisfied. Moreover, quark-antiquark contributions in the region $-ξ<x<ξ$ are non-vanishing. Our results are qualitatively similar to those calculated with Radyushkin's double distribution ansatz using forward parton distribution functions calculated in the NJL model as inputs.

hep-ph↗

arXiv2004

Neutron Star Properties from an NJL Model Modified to Simulate Confinement

The NJL model has recently been extended with a method to simulate confinement. This leads in mean field approximation to a natural mechanism for the saturation of nuclear matter. We use the model to investigate the equation of state of asymmetric nuclear matter and then use it to compute the properties of neutron stars.

nucl-th↗

arXiv2004

The relation between the photonuclear E1 sum rule and the effective orbital g-factor

The connection between the enhancement factor (1+kappa) of the photonuclear E1 sum rule and the orbital angular momentum g-factor (gl) of a bound nucleon is investigated in the framework of the Landau-Migdal theory for isospin asymmetric nuclear matter. Special emphasis is put on the role of gauge invariance to establish the kappa-gl relation. By identifying the physical processes which are taken into account in kappa and gl, the validity and limitations of this relation are discussed. The connections to the collective excitations and to nuclear Compton scattering are also shown.

nucl-th↗

arXiv2003

Quark distributions in nuclear matter and the EMC effect

Quark light cone momentum distributions in nuclear matter and the structure function of a bound nucleon are investigated in the framework of the Nambu-Jona-Lasinio model. This framework describes the nucleon as a relativistic quark-diquark state, and the nuclear matter equation of state by using the mean field approximation. The scalar and vector mean fields in the nuclear medium couple to the quarks in the nucleon and their effect on the spin independent nuclear structure function is investigated in detail. Special emphasis is placed on the important effect of the vector mean field and on a formulation which guarantees the validity of the number and momentum sum rules from the outset.

nucl-th↗

arXiv2002

Phase transition from nuclear matter to color superconducting quark matter

We construct the nuclear and quark matter equations of state at zero temperature in an effective quark theory (the Nambu-Jona-Lasinio model), and discuss the phase transition between them. The nuclear matter equation of state is based on the quark-diquark description of the single nucleon, while the quark matter equation of state includes the effects of scalar diquark condensation (color superconductivity). The effect of diquark condensation on the phase transition is discussed in detail.

nucl-th↗

arXiv2002

Axial vector diquark correlations in the nucleon: Structure functions and static properties

In order to extract information on the strength of quark-quark correlations in the axial vector (a.v.) diquark channel ($J^P=1^+, T=1$), we analyze the quark light cone momentum distributions in the nucleon, in particular their flavor dependencies, and the static properties of the nucleon. To construct the nucleon as a relativistic 3-quark bound state, we use a simple 'static' approximation to the full Faddeev equation in the Nambu-Jona-Lasinio model, including correlations in the scalar ($J^P=0^+, T=0$) and a.v. diquark channels. It is shown that the a.v. diquark correlations should be rather weak compared to the scalar ones. From our analysis we extract information on the strength of the correlations as well as on the probability of the a.v. diquark channel.

nucl-th↗

arXiv2001

The Stability of Nuclear Matter in the Nambu-Jona-Lasinio Model

Using the Nambu-Jona-Lasinio model to describe the nucleon as a quark-diquark state, we discuss the stability of nuclear matter in a hybrid model for the ground state at finite nucleon density. It is shown that a simple extension of the model to simulate the effects of confinement leads to a scalar polarizability of the nucleon. This, in turn, leads to a less attractive effective interaction between the nucleons, helping to achieve saturation of the nuclear matter ground state. It is also pointed out that that the same effect naturally leads to a suppression of ``Z-graph'' contributions with increasing scalar potential.

nucl-th↗

arXiv1999

Quark distrbutions in the nucleon based on a relativistic 3-body approach to the NJL model

Quark light cone momentum distributions in the nucleon are calculated in a relativistic 3-body approach to the NJL model by using a simple 'static approximation' for the Faddeev kernel. A method is presented which automatically satisfies the number and momentum sum rules, even in the regularized theory. In order to assess the sensitivity to the regularization scheme, two schemes which can be formulated in terms of light cone variables are discussed. The effects of the (composite) pion cloud are taken into account in a convolution approach, and the violation of the Gottfried sum rule is discussed. After performing the Q^2 evolution, the resulting distributions are compared to the empirical ones.

nucl-th↗

arXiv1999

NJL model on the light cone and pion structure function

The NJL model is formulated on the light cone. Using the 1/N expansion to solve the fermionic constraint, an effective 4-fermi lagrangian is derived. Pionic properties are investigated using this lagrangian, and the formal equivalence to the equal-time formulation is demonstrated. Two regularization schemes in terms of light-cone variables are discussed: An extension of the 'invariant mass cut-off scheme', and a transverse momentum cut-off scheme. It is shown that the first one is equivalent to the covariant 3-momentum cut-off (dispersion cut-off) scheme in the equal-time formulation. As an application the structure function of the pion is studied in both regularization schemes.

hep-ph↗

arXiv1994

Elimination of the Landau Ghost from Chiral Solitons

We show a practical way based on the Källén-Lehmann representation for the two-point functions to eliminate the instability of the vacuum against formation of small sized meson configurations in the chiral $σ$ model.

hep-ph↗