Meson exchange model for pseudoscalar meson-meson scattering

A dynamical model for pseudoscalar-pseudoscalar meson scattering based on meson exchange, suitable for use in a variety of low- and intermediate-energy mesonic interactions, has been constructed and applied to ππ and kπ scattering with good quantitative results. The model includes both s- and t-channel exchange, and is found to require pseudoscalar-pseudoscalar coupling to a scalar octet to fit the high energy s-wave phases in the I = 0 ππ channel and in the channel. Coupling of the ππ and KK̄ channels is found to play a crucial role in explaining the S∗(975) resonanc

On the nature of the residual meson-meson interaction from simulations with a QED2+1{}_{2+1} model

A potential between mesons is extracted from 4-point functions within lattice gauge theory taking 2+1 dimensional QED as an example. This theory possesses confinement and dynamical fermions. The resulting meson-meson potential has a short-ranged hard repulsive core and the expected dipole-dipole forces lead to attraction at intermediate distances. Sea quarks lead to a softer form of the total potential.Comment: 4 pages, uuencoded tar-compressed postscript file, contribution to Lattice'9

Meson-meson correlations in baryon-baryon and antibaryon-baryon interactions

Recent work of the J\"ulich group about the role of meson-meson correlations in baryon-baryon and antibaryon-baryon interactions is reviewed.Comment: Lecture given at the Erice School 1995, TEX, 10 pages, 15 figure

Baryon-Baryon Potentials on the Lattice

The interaction of spatially extended heavy baryons is investigated in the framework of lattice QCD with dynamical quarks. It is shown that the expected dipole forces have a very short range and that the baryon-antibaryon interaction is more attractive than the baryon-baryon interaction. Sea quarks play a minor important role.Comment: 8 pages, uuencoded postscript file; Physics Letters B, in pres

Relativistic structure of one-meson and one-gluon exchange forces and the lower excitation spectrum of the Nucleon and the Delta

The lower excitation spectrum of the nucleon and $\Delta$ is calculated in a relativistic chiral quark model. Corrections to the baryon mass spectrum from the second order self-energy and exchange diagrams induced by pion and gluon fields are estimated in the field -theoretical framework. Convergent results for the self-energy terms are obtained when including the intermediate quark and antiquark states with a total momentum up to $j=25/2$. Relativistic one-meson and color-magnetic one-gluon exchange forces are shown to generate spin 0, 1, 2, etc. operators, which couple the lower and the upper components of the two interacting valence quarks and yield reasonable matrix elements for the lower excitation spectrum of the Nucleon and Delta. The only contribution to the ground state nucleon and $\Delta$ comes from the spin 1 operators, which correspond to the exchanged pion or gluon in the l=1 orbit, thus indicating, that the both pion exchange and color-magnetic gluon exchange forces can contribute to the spin of baryons. Is is shown also that the contribution of the color-electric component of the gluon fields to the baryon spectrum is enormously large (more than 500 MeV with a value $\alpha_s=0.65$) and one needs to restrict to very small values of the strong coupling constant or to exclude completely the gluon-loop corrections to the baryon spectrum. With this restriction, the calculated spectrum reproduces the main properties of the data, however needs further contribution from the two-pion exchange and instanton induced exchange (for the nucleon sector) forces in consistence with the realistic NN-interaction models.Comment: 15 pages, 4 figures, 7 table

Extraction of hadron-hadron potentials on the lattice within 2+1 dimensional QED

A potential between mesons is extracted from 4-point functions within lattice gauge theory taking 2+1 dimensional QED as an example. This theory possesses confinement and dynamical fermions. The resulting meson-meson potential has a short-ranged hard repulsive core due to antisymmetrization. The expected dipole-dipole forces lead to attraction at intermediate distances. Sea quarks lead to a softer form of the total potential.Comment: 12 pages, uuencoded tar-compressed postscript fil

Modelling nucleon-nucleon scattering above 1 GeV

Motivated by the recent measurement of proton-proton spin-correlation parameters up to 2.5 GeV laboratory energy, we investigate models for nucleon-nucleon (NN) scattering above 1 GeV. Signatures for a gradual failure of the traditional meson model with increasing energy can be clearly identified. Since spin effects are large up to tens of GeV, perturbative QCD cannot be invoked to fix the problems. We discuss various theoretical scenarios and come to the conclusion that we do not have a clear phenomenological understanding of the spin-dependence of the NN interaction above 1 GeV.Comment: 36 pages, 8 figure

Role of correlated two-pion exchange in K+NK^+ N scattering

A dynamical model for S-- and P--wave correlated $2 \pi$ (and $K \bar K$) exchange between a kaon and a nucleon is presented, starting from corresponding $N \bar N \rightarrow K \bar K$ amplitudes in the pseudophysical region, which have been constructed from nucleon, $\Delta$--isobar and hyperon ($\Lambda$, $\Sigma$) exchange Born terms and a realistic meson exchange model of the $\pi \pi \rightarrow K \bar K$ and $K \bar K \rightarrow K \bar K$ amplitude. The contribution in the s--channel is then obtained by performing a dispersion relation over the unitarity cut. In the $\rho$--channel, considerable ambiguities exist, depending on how the dispersion integral is performed. Our model, supplemented by short range interaction terms, is able to describe empirical $K^+ N$ data below pion production threshold in a satisfactory way.Comment: 24 pages, REVTEX, figures available from the author