K. Rabitsch

Evidence for quantum chaos in the plasma phase of QCD

Abstract We investigate the eigenvalue spectrum of the staggered Dirac matrix in SU(3) gauge theory and in full QCD on a 6 3 ×4 lattice. As a measure of the fluctuation properties of the eigenvalues, we study the nearest-neighbor spacing distribution P ( s ) for various values of β both in the confinement and in the deconfinement phase. In both phases except far into the deconfinement region, the lattice data agree with the Wigner surmise of random-matrix theory which is indicative of quantum chaos. We do not find signs of a transition to Poisson regularity at the deconfinement phase transition.

Exploring the π+-π+ Interaction in Lattice QCD

Abstract. An effective residual interaction for a meson-meson system is computed in lattice QCD. We describe the theoretical framework and present its application to the I = 2 channel S-wave interaction of the π-π system. Scattering phase shifts are also computed and compared to experimental results.

Forces between composite particles in QCD

Abstract Starting from the meson-meson Green function in 3+1 dimensional quenched lattice QCD we calculate potentials between heavy-light mesons for various light-quark mass parameters. For the valence quarks we employ the staggered scheme. The resulting potentials turn out to be short ranged and attractive. A comparison with a tadpole improved action for the gauge field is presented.

On the I = 2 channel π-π interaction in the chiral limit☆

Abstract An approximate local potential for the residual π+-π+ interaction is computed. We use an O(a2) improved action on a coarse 93 × 13 lattice with 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 π+-π+ potential to the chiral limit.

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

Abstract 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 (π-π) 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.

Baryon-baryon potentials on the lattice☆

Abstract 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.

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.

Quantum chaos in QCD at finite temperature

Abstract We study complete eigenvalue spectra of the staggered Dirac matrix in quenched QCD on a 63 × 4 lattice. In particular, we investigate the nearest-neighbor spacing distribution P(s) for various values of β 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.

Interactions of Pion-like Particles from Lattice QCD

An approximate local potential for the residual π+ - π+ interaction is computed. We use an O(a 2) improved action on a coarse 93 x 13 lattice with spacing a ≈ 0.4fm. We attempt extrapolation of the π+ - π+ potential to the chiral limit.

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

Abstract 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(a2) 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 potentials.