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

Two-body spectra of pseudoscalar mesons with an O(a2)O(a^2)--improved lattice action using Wilson fermions

We extend our calculations with the second-order tree-level and tadpole improved next-nearest-neighbor action to meson-meson systems. Correlation matrices built from interpolating fields representing two pseudoscalar mesons (pion-pion) with relative momenta p are diagonalized, and the mass spectrum is extracted. Link variable fuzzing and operator smearing at both sinks and sources is employed. Calculations are presented for two values of the hopping parameter. The spectrum is used to discuss the residual interaction in the meson-meson system.Comment: 3 pages, 4 EPS figures, Poster presented at "Lattice'97", to appear in the proceeding

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

Quantum chaos in QCD at finite temperature

We study complete eigenvalue spectra of the staggered Dirac matrix in quenched QCD on a $6^3\times 4$ lattice. In particular, we investigate the nearest-neighbor spacing distribution $P(s)$ for various values of $\beta$ both in the confinement and deconfinement phase. In both phases except far into the deconfinement region, the data agree with the Wigner surmise of random matrix theory which is indicative of quantum chaos. No signs of a transition to Poisson regularity are found, and the reasons for this result are discussed.Comment: 3 pages, 6 figures (included), poster presented by R. Pullirsch at "Lattice 97", to appear in the proceeding

Potentials between heavy-light mesons from lattice and inverse scattering theory

We extend our investigation of heavy-light meson-meson interactions to a system consisting of a heavy-light meson and the corresponding antiparticle. An effective potential is obtained from meson-antimeson Green-functions computed in a quenched simulation with staggered fermions. Comparisons with a simulation using an $O(a^2)$ tree-level and tadpole improved gauge action and a full QCD simulation show that lattice discretization errors and dynamical quarks have no drastic influence. Calculations from inverse scattering theory propose a similar shape for $K\bar{K}$ potentials.Comment: 3 pages, 5 EPS figures, Poster presented at "Lattice'97", to appear in the proceeding

Quantum chaos and QCD at finite chemical potential

We investigate the distribution of the spacings of adjacent eigenvalues of the lattice Dirac operator. At zero chemical potential $\mu$, the nearest-neighbor spacing distribution $P(s)$ follows the Wigner surmise of random matrix theory both in the confinement and in the deconfinement phase. This is indicative of quantum chaos. At nonzero chemical potential, the eigenvalues of the Dirac operator become complex. We discuss how $P(s)$ can be defined in the complex plane. Numerical results from an SU(3) simulation with staggered fermions are compared with predictions from non-hermitian random matrix theory, and agreement with the Ginibre ensemble is found for $\mu\approx 0.7$.Comment: LATTICE98(hightemp), 3 pages, 10 figure

Meson-meson interactions -- from static to dynamic valence quarks

A method for the extraction of an effective meson-meson potential from Green functions, which can be obtained from a lattice simulation, is presented. Simulations are carried out for compact QED and QCD in four dimensions using the quenched approximation and the hopping parameter expansion. In a further study, a heavy-light meson is considered employing a conjugate gradient algorithm for the light propagators. Due to the Pauli exclusion principle, the results for QED indicate the existence of a hard core, but for QCD there is strong attraction at small meson distances.Comment: 4 pages, uuencoded gziped postscript file, contribution to LATTICE'95, Melbourne, Australia (list of authors completed

On the I=2 channel pi-pi interaction in the chiral limit

An approximate local potential for the residual pi+ pi+ interaction is computed. We use an O(a**2) improved action on a coarse 9x9x9x13 lattice with approximately a=0.4fm. The results present a continuation of previous work: Increasing the number of gauge configurations and quark propagators we attempt extrapolation of the pi+ pi+ potential to the chiral limit.Comment: LATTICE98(spectrum) LaTeX2e, 3 pages, 3 eps figure