The quark compound bag model: Defining the admixture of six-quark bag in the deuteron

The probability of the six-quark bag part of the deuteron is defined within recently formulated quark compound bag (QCB) model. An upper limit of about 1 % for the admixture of the confined bag in the deuteron is found for the QCB potential supplied by the long range Paris interaction. The six-quark bag corrections to the static multipole moments of the deuteron are estimated to be ?1 % forμ _d and ?6% forQ _d .     

Nucleon-nucleon interaction with tensor forces in the quark compound bag model

A model forN-N interaction proposed earlier by two of us (VSB and VKG), has been extended to incorporate the tensor component of the nuclear force. Based on the quark compound bag model (QCB), the nucleon-nucleon potential has a short range repulsive core which is non-local and has a characteristic energy dependence and is expressed in terms of the parameters relating to the six-quark compound bag. To account for the low energy properties, this repulsive core interaction is supplemented by a phenomenological non-local potential containing both central (S-wave) and tensor components and operates only outside the QCB. Using this model, we analyse and compare the results with the experimental data for the electromagnetic form factors of the deuteron, theD-state observables, such as the quadrupole moment, theD-state probability, and theD/S ratio along with then-p scattering phase shifts up to about 400 MeV.     

1S0 and 3S13D1 nucleon-nucleon potentials in the quark compound bag model

For nucleons interacting via formation of the quark compound bag the resulting potential is written in a general form. Explicit examples of potentials are constructed in the ¹S₀, ³S₁ and ³S₁-³D₁ states fitted to the experimental data at T_L ? 1 GeV. As an outcome the QCB energy levels (dibaryons) and NN admixture in QCB are obtained in good agreement with theoretical predictions.     

Dispersion-relation analysis of K+p scattering below 2 GeV/c

We have obtained K⁺p scattering amplitudes that fit a large body of data below 2 GeV/c, satisfy phenomenological partial-wave backward dispersion relations, and are consistent with forward dispersion relations for the spin-non-flip amplitude, and forward dispersion-relation sum rules for the K⁺p P-wave scattering lengths. This has been achieved by firstly making an energy-dependent phase-shift analysis of 1 660 pieces of K⁺p data below 2 GeV/c, using parameterised partial-wave dispersion relations, with the additional constraints of forward dispersion relations and P-wave scattering lengths obtained from forward dispersion-relation sum rules, and then checking the resulting solutions for consistency with backward K⁺p dispersion relations.     

QCD coupling constant below 1 GeV in the poincare-covariant model

The behavior of the running coupling constant α _s (Q ²) phenomenologically parameterized in the region of Q < 1 GeV is considered within the framework of the Poincare-covariant quark model in a variety of regimes. An analysis was carried out for pseudoscalar and vector mesons with the lepton masses and decay constants (obtained by the model calculations) required to match their experimental counterparts. It shows that the constant α _s is likely to behave with α_crit = α _s (Q ² = 0) ∼ 0.667 − 0.821 in the case of a frozen regime and α_crit =0.300 − 0.692 for peaked curves, which follows from the experimental values of the leptonic decay constants and masses.     

Dilepton production in nucleon-nucleon collisions around 1 GeV/nucleon: A theoretical update

We present a fully relativistic and gauge invariant framework for calculating the cross-sections of dilepton production in nucleon-nucleon (NN) collisions which is based on the meson-exchange approximation for the NN scattering amplitudes. Predictions of our model are compared with those of other covariant models that have been used to describe this reaction. We discuss the comparison of our calculations with the old DLS and the recent HADES data.     

Quark cluster model and the R-matrix theory treatment of NN scattering

A microscopic quark cluster model has been developed for six-quark states consisting of two s³ quark clusters. The consequences of channel nonorthogonality and existence of Pauliforbidden states are investigated explicitly by solving the eigenvalue problem of the resonating group method (RGM) kernel. Since the RGM kernels needed are all available, the form of the six-quark states given in this paper is very suited to detailed RGM calculations. A rigorous treatment based on the R-matrix theory has been carried out to obtain NN phase shifts. The spin-spin term of the quark-quark interaction favors states of higher color-spin symmetry. This explains the larger change caused by the hidden color states in the ³S₁ phase shifts than in the ¹S₀ phase shifts. Phase shifts calculated with inclusion of the delta and hidden color states are still too repulsive. It is pointed out that there arises a subtle problem in adding the one-boson exchange potential by hand to the RGM equation.     

Proton-nucleus elastic scattering at 1 GeV in the glauber model

Differential elastic cross sections and polarizations are calculated in a multiple-scattering formalism for proton-nucleus scattering at 1 GeV incident energy. The calculations include Coulomb and spin effects. Corrections to the Glauber model are studied. It is shown that for momentum transfer up to 2.0–2.5 fm^?1 the reaction mechanism can be taken with confidence. Consequently, fits to the experimental data over this limited range in q can be considered to extract nuclear structure information. In the present case, use has been made of nuclear densities arising from self-consistent calculations. The calculations are compared with experimental data.     

A new path-integral representation of the T-matrix in potential scattering

We employ the method used by Barbashov and collaborators in Quantum Field Theory to derive a path-integral representation of the T-matrix in nonrelativistic potential scattering which is free of functional integration over fictitious variables as was necessary before. The resulting expression serves as a starting point for a variational approximation applied to high-energy scattering from a Gaussian potential. Good agreement with exact partial-wave calculations is found even at large scattering angles. A novel path-integral representation of the scattering length is obtained in the low-energy limit.     

K+N scattering in the constituent quark model

We calculate S-wave phase shifts of the KN system in the framework of a nonrelativistic quark model, using variational methods (generator coordinates). We show that the I = 0 channel is determined by the QCD residual interaction, which leads to a small repulsion, and that the I = 1 channel receives strong repulsive contributions already from quark exchange. We discuss the relevance and physical origin of these results. We furthermore construct an approximate local potential extracted from the nonlocal cluster interaction.     

A fundamental theory of the half-shell t-matrix for nucleon-nucleon scattering

A dispersion-theoretic approach to the half-shell t-matrix is presented and applied to the ¹S₀- and ¹P₁-Reid interactions. This approach is shown to provide interesting dynamical insights about these half-shell t-matrices.     

Dynamical study of light scalar mesons below 1 GeV in a flux-tube model

The light scalar mesons below 1GeV configured as tetraquark systems are studied in the framework of the flux-tube model. Comparative studies indicate that a multi-body confinement,instead of the additive two-body confinement, should be used in a multiquark system.The σ and κ mesons could be well accommodated in the diquark-antidiquark tetraquark picture, and could be colour-confinement resonances. The a0(980) and fo(980) mesons are not described as KK molecular states and ns diquark-antidiquark states.However, the mass of the first radial excited state of the diquark-antidiquark state, nn is 1019 MeV,is close to the experimental data of the fo (980).     

An analysis of some proton-nucleus scattering data at 1 GeV

The elastic and inelastic scattering data of 1 GeV protons on ¹²C, ³⁹K,^{40, 48}Ca, ⁵⁸Ni and ²⁰⁸Pb are analysed within the framework of Glauber theory. The collective excitations to one-phonon levels are treated using the Tassie model under the adiabatic approximation. Effects of both the coupling between the elastic and the inelastic channels and the two-body correlation in the intrinsic state are considered. The ground state and transition densities for the protons are taken from electron scattering experiments and appropriate assumptions for the neutron densities are made. In most of the cases, better agreement with the experimental data than reported in earlier analyses is obtained. The effects of the coupling and the pair correlation seem to be important only for ¹²C. The elastic data strongly indicate that the density distributions for protons and neutrons in ⁴⁸Ca and ²⁰⁸Pb are different. In ⁴⁸Ca, the surface envelope of the neutron distribution is found to be the same as for the proton distribution but is placed at a larger radius. On the other hand, the neutron distribution in ²⁰⁸Pb seems to be relatively much more diffuse.     

Divergence of the quark self-energy in the second quantized chiral bag model

When summing over the intermediate quark states of a spherical cavity, the quark self-energy of the chiral bag model, in lowest order of the pion coupling, is shown to generate a series of terms, each one growing linearly with the angular variable κ. However, there is a cancellation between terms for different κ, which finally leads to an overall linearly divergent series.     

The real part of the forward scattering amplitude in π±p elastic scattering below 2 GeV/c

The differential cross section for π^±p elastic scattering below 2 GeV/c has been measured at small forward pion angles by an electronics experiment. The interference effects observed between the Coulomb and the nuclear interaction have been used to determine the magnitude and sign of the real parts of the π^±p forward scattering amplitude. The latter are compared to the values predicted by the dispersion relations.     

Elastic scattering of α particles on light nuclei at Pα=7 GeV/c

Elastic scattering differential cross sections of α particles have been measured at P_α=7.0 GeV/c ($\text{T}\text{N}\text{=1.05}\text{GeV}$) on ¹H, ²H, ³He and ⁴He target up to a momentum transfer of ～4 (GeV/c)². A preliminary interpretation of the data is given in the framework of the Glauber theory.     

T-matrix method and its applications to electromagnetic scattering by particles: A current perspective

This note serves as a short introduction to the reprint of our article “T-matrix computations of light scattering by nonspherical particles: a review” (JQSRT 1996; 55:535-75). We first discuss the motivation for writing that article and explain its historical context. This is followed by a short overview of more recent developments.     

Complete S-matrix of the massive thirring model

On the basis of Zamolodchikov's S-matrix for two sine-Gordon solitons we derive the S-matrix for the scattering of an arbitrary number of particles including bound states.