The pi-N Sigma term - a lattice investigation

A lattice calculation of the pi-N sigma term is described using dynamical staggered fermions. Preliminary results give a sea term comparable in magnitude to the valence term.Comment: Latex article. 6 pages, uuencoded compressed tar file. Contribution to the Kyffhaeuser Workshop (Leipzig, Germany, September 1993). HLRZ preprint 93-6

The ``Spin'' Structure of the Nucleon - a lattice investigation

We will discuss here an indirect lattice evaluation of the baryon axial singlet current matrix element. This quantity may be related to the fraction of nucleon spin carried by the quarks. The appropriate structure function has recently been measured (EMC experiment). As in this experiment, we find that the quarks do not appear to carry a large component of the nucleon spin.Comment: Latex article. 3 pages. Contribution to the Second IMACS Conference on Computational Physics, Cahokia, U.S.A. October 1993. HLRZ preprint 93-7

Effective Yukawa Couplings in Noncompact Lattice QED

We investigate effective Yukawa couplings of mesons to the elementary fermions in noncompact lattice QED. The couplings are extracted from suitable fermion-antifermion-meson three-point functions calculated by Monte Carlo simulations with dynamical staggered fermions. The scaling behaviour is compatible with expectations from perturbation theory, thus indicating triviality of QED. The lines of constant Yukawa coupling are compared to flows of other quantities. Consistency is seen, at most, for weak coupling.Comment: 12 pages, uuencoded compressed postscrip

Is the Chiral Phase Transition in Non-Compact Lattice QED Driven by Monopole Condensation?

We investigate the recent conjecture that the chiral phase transition in non-compact lattice QED is driven by monopole condensation. The comparison of analytic and numerical results shows that we have a quantitative understanding of monopoles in both the quenched and dynamical cases. We can rule out monopole condensation.Comment: 21 pages, 10 postscript figures include

The SU(3) Beta Function from Numerical Stochastic Perturbation Theory

The SU(3) beta function is computed from Wilson loops to 20th order numerical stochastic perturbation theory. An attempt is made to include massless fermions, whose contribution is known analytically to 4th order. The question whether the theory admits an infrared stable fixed point is addressed.Comment: 10 pages, 7 figures, version to be published in Physics Letters

Hadronic coupling constants in lattice QCD

We report on calculations of the hadronic coupling constants $g_{\rho\pi\pi}$ and $g_{nn\pi}$ based on lattice QCD with four flavors of dynamical staggered fermions. By computing 2--point and 3--point Green's functions we have been able to determine these coupling constants ab initio from QCD; the results are compatible with the experimental values.Comment: 3 Page