Soliton Bag Model Research Articles

Self-consistent one-gluon exchange in soliton bag models

The treatment of soliton bag models as two-point boundary value problems is extended to include self-consistent one-gluon exchange interactions. The colour-magnetic contribution to the nucleon-delta mass splitting is calculated self-consistently in the mean-field, one-gluon-exchange approximation for the Friedberg-Lee and Nielsen-Patkos models. Small glueball mass parameters ( m GB∼500 MeV) are favoured. Comparisons with previous calculations are made.

Bag-model nuclear equation of state in the Wigner-Seitz approximation.

The nuclear equation of state is calculated using the soliton bag model and the Wigner-Seitz approximation for baglike states on a lattice. Since the Wigner-Seitz treatment averages over lattice structure, it is more realistic for a fluid like nuclear matter than is a periodic crystal model. A crucial feature of the model presented here is the manner of filling the Bloch band of independent particle states: We argue for a dilute filling of the entire band. Quark wave functions sigma field configurations, and energies are calculated as a function of baryon density. The energies are only qualitatively similar to semiempirical nuclear energies. Within the context of this crude model, we find a first-order phase transition corresponding to a nuclear matter phase which sets in at about six times normal density and a plasma phase at roughly 12 times normal nuclear density.

Chiral nontopological solitons with perturbative quantum pions.

We investigate chiral extensions of a broad class of nontopological soliton bag models. Chiral symmetry is restored in a nonlinear realization through the introduction of an elementary pion field. We show in particular that it is consistent to treat the pions as a perturbative quantum field, as is done in the cloudy-bag model. The cloudy-bag model is recovered as a limiting case. A careful comparison is made between predictions of chiral extensions of the Friedberg-Lee and the Nielsen-Patkos color-dielectric nontopological soliton models and the cloudy-bag model. Once the overall distance scale is fixed we find relative insensitivity to the detailed choice of nontopological soliton parameters. We investigate two versions of chiral nontopological solitons, analogous to the surface- and volume-coupled cloudy-bag model, and discuss their relation to current algebra.

Surface Collective Motion in the Soliton Bag Model

Surface Collective Motion in the Soliton Bag Model

Quarks and the saturation properties of nuclear matter.

A two-region model of the nuclear force is developed by using quark degrees of freedom at short ranges and nucleons elsewhere. In the quark sector, the soliton bag model and generator coordinates are used so that the quark fields undergo a continuous deformation as the two nucleons overlap. This model describes the spin singlet nucleon-nucleon scattering data very well. The density and binding energy of nuclear matter are also computed in lowest-order Brueckner theory. Quark effects are found to decrease both the saturation density and binding energy.

Surface collective motion in the soliton bag model

Surface monopole vibration of the baryon is investigated on the basis of the soliton bag model. We derive a relativistic lagrangian for the motion, of which the mass parameter is proportional to the square of the bag radius. With the use of the semi-classical quantization, the energy spectra of the P 11 and P 33 resonances are reproduced fairly well by our model.

Self-consistent treatment of one-gluon exchange in the soliton bag model

In the context of the soliton bag model, the quarks, soliton field and the gluon propagator are calculated self-consistently in the mean-field, one-gluon exchange approximation. The use of a confined propagator, as compared with a free propagator, is primarily to change the effective quark-gluon coupling constant by a factor of approximately two in the case of static, spherical bags. Self-consistency leads to only a small improvement in the fit to physical data, after readjustment of model parameters. Nevertheless, use of a confined propagator is expected to have an important effect on deformed bags and in dynamical calculations.

Phase transition in the soliton bag model

The soliton bag model is studied at finite temperature and zero baryon density. The authors work in the one-loop approximation, including both quark and sigma loops. A phase transition occurs at a temperature approximately 100 MeV (for three light quark flavours). The dependence of the transition temperature on the model parameters is presented. They find that the model allows for the possibility of super-cooled and super-heated metastable phases.

Soliton bag model with scalar mesons

We propose a soliton bag model with scalar mesons which is a modification of the simple soliton bag model and the linear sigma model. Our model can give comparatively large quark mass, so that it is applicable to low energy scattering. We have solved the Euler-Lagrange equations in the mean-field approximation for the hedgehog baryon state. The static properties of the nucleon is calculated by a projection method. Our results are in reasonable agreement with the observed values.

Low-energy meson action from QCD: Extended Skyrme model.

In the limit of extremely low energies QCD describes essentially the interactions between the approximately massless pseudoscalars. They are the bound states of the ''chiral'' quarks. Equivalently they are collective Goldstone modes of dynamically broken chiral symmetry, and interact in a nonlinear way with the ''constituent'' quarks. These two pictures are related by going into the ''constituent gauge,'' which we define in this paper as a QCD analog of the unitary gauge in theories with Higgs scalars. We develop a framework for extracting the low-energy dynamics of pions directly from QCD in the limit of a large number of colors, and under some additional assumptions we calculate the pure pion theory truncated to four derivatives. The model obtained is a somewhat extended Skyrme model, and contains the anomaly term (Wess-Zumino term) as well as the nontopological terms, the coefficients of which depend on a classical scalar-meson-field background. Stability of the soliton is discussed. We show that in the limit in which symmetry breaking is turned off, the coefficients in front of the pseudoscalar interactions vanish. Under a plausible assumption about the behavior of a scalar-meson background, we interpret this as a natural realization of the space cutoff entering the topologicalmore » soliton bag model.« less

Constant chromomagnetic field in the soliton bag model.

In the Friedberg-Lee soliton bag model, a potential function may be found such that the chromomagnetic field generated by each quark is constant. The coupled field equations of the soliton bag model then reduce to a single second-order differential equation depending on only one parameter. The values obtained for static baryonic observables, for the effective strong fine-structure constant, and for the scalar-glueball mass agree well with present knowledge.

Hadron static properties obtained from soliton bag model with iterative one-gluon exchange

The one-gluon exchange is iterated self-consistently within the framework of the Friedberg-Lee soliton bag model. While the parameters of the model are determined from fitting only the nucleon mass, the delta mass and the proton r.m.s. charge radius, the model is able to predict the static properties of other baryons and mesons, which compare favorably with the available experimental data. Eesults obtained in the self-consistent iterative approach differ significantly from those given by the calculations in which one-gluon exchange is only treated perturbatively. In particular, the iterative one-gluon exchange can lead to a light pion mass and to improved charge form factors.

Soliton bag model

The soliton bag model of Friedberg and Lee is motivated as a model of long range behavior of QCD. Some numerical results for the nucleon are presented. The question of Lorentz covariance and future trends in bag model physics are explored.

Pion as aqq¯soliton bag: Dressing of the nucleon andΔ

The pion cloud surrounding the nucleon and the ..delta.. is studied in the soliton bag model. The quark-antiquark substructure of the pion is fully taken into account using generator-coordinate techniques. The one-gluon-exchange piece of the model Hamiltonian is responsible for creating the q-italicq-bar pair. The results we obtain for various hadronic properties are in good agreement with experimental data and qualitatively similar to those obtained in the cloudy bag model.

Nucleon-nucleon scattering in the soliton bag model

The soliton bag model introduced by Friedberg and Lee is applied to nucleon-nucleon scattering. The dynamics of six quarks and their confining soliton field is treated in the generator coordinate method. The potential obtained in an effective Schrödinger equation substantially differs from the results of adiabatic calculations.

Dynamical bag constant and surface tension of baryon droplets at finite temperature and density

From the non-topological soliton bag model a droplet model for baryons at finite temperature and density is constructed. The resulting surface tension and dynamical bag constant is calculated as a function of temperature and density.

Kaluza, Klein, confinement, and nuclear forces

The nonsymmetric Kaluza-Klein and Jordan-Thiry theories are reviewed as interesting propositions of physics in higher dimensions. It is shown how a dielectric model of confinement can be derived from “interference effects” in these theories. It is postulated that the old puzzle of nuclear physics,σ-particles, can be connected to the skewon fieldg[μv] and the scalar field Ψ in the nonsymmetric Jordan-Thiry theory. Similarities are pointed out between the nonsymmetric Jordan-Thiry Lagrangian in the flat space limit and the soliton bag model Lagrangian. Finally the nonsymmetric Jordan-Thiry Lagrangian is proposed as the bosonic part of the strong interaction Lagrangian.

Lattice QCD and the soliton bag model

The parameters of the soliton bag model of Friedberg and Lee can be related to the following results of lattice gauge theory: transition temperature T c, string constant E l , and glueball mass m GB.

Momentum projection and relativistic boost of solitons: Coherent states and projection.

We present a method for calculating center-of-mass corrections to hadron properties in soliton models and we apply the method to the soliton bag model. A coherent state is used to provide a quantum wave function corresponding to the mean-field approximation. This state is projected onto a zero-momentum eigenstate. States of nonzero momentum can be constructed from this with a Lorentz boost operator. Hence center-of-mass corrections can be made in a properly relativistic way. The energy of the projected zero-momentum state is the hadron mass with spurious center-of-mass energy removed. We apply a variational principle to our projected state and use three ``virial theorems'' to test our approximate solution. We also study projection of general one-mode states. Projection reduces the nucleon energy by up to 25%. Variation after projection gives a further reduction of less than 20%. Somewhat larger reductions in the energy are found for meson states.

Quark-soliton model of nucleon structure and reactions

A summary of recent and current research on the Soliton Bag Model is presented. The unique feature of the model, namely dynamics, is emphasized, since this permits calculation of reactions within the frame-work of the covariant effective Lagrangian. One gluon exchange effects are included.