Yang-Mills instanton as a quantum black hole

In terms of spin-charge separated variables, the Minkowski space Yang-Mills BPST instanton describes a locally conformally flat doubly-wrapped cigar manifold that can be viewed as a Euclidean quantum black hole. An ensemble of instantons then corresponds to a ``spacetime foam'' that creates a locally conformally flat spacetime from ``nothing'' as a quantum fluctuation.Comment: 11 pages, revise

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

Perturbative renormalisation of quark bilinear operators for overlap fermions with and without stout links and improved gauge action

We calculate lattice renormalisation constants of local and one-link quark operators for overlap fermions and improved gauge actions in one-loop perturbation theory. For the local operators we stout smear the SU(3) links in the fermionic action. Using the popular tadpole improved L\"uscher-Weisz actions at $\beta=8.45$ and $\beta=8.0$ we present numerical values for the Z factors in the $\bar{MS}$ scheme (partly as function of the stout smearing strength). We compare various levels of mean field (tadpole) improvement which have been applied to our results.Comment: 7 page

Scaling of Non-Perturbatively O(a) Improved Wilson Fermions: Hadron Spectrum, Quark Masses and Decay Constants

We compute the hadron mass spectrum, the quark masses and the meson decay constants in quenched lattice QCD with non-perturbatively $O(a)$ improved Wilson fermions. The calculations are done for two values of the coupling constant, $\beta = 6.0$ and 6.2, and the results are compared with the predictions of ordinary Wilson fermions. We find that the improved action reduces lattice artifacts as expected

Non-Perturbative versus Perturbative Renormalization of Lattice Operators

Our objective is to compute the moments of the deep-inelastic structure functions of the nucleon on the lattice. A major source of uncertainty is the renormalization of the lattice operators that enter the calculation. In this talk we compare the renormalization constants of the most relevant twist-two bilinear quark operators which we have computed non-perturbatively and perturbatively to one loop order. Furthermore, we discuss the use of tadpole improved perturbation theory.Comment: 4 pages, uuencoded postscript file. Contribution to Lattice 95. Also available from http://www.desy.de/pub/preprints/desy/199