On the existence of a first order phase transition at small vacuum angle θ\theta in the CP3CP^3 model

We examine the phase structure of the $CP^3$ model as a function of $\theta$ in the weak coupling regime. It is shown that the model has a first order phase transition at small $\theta$. We pay special attention to the extrapolation of the data to the infinite volume. It is found that the critical value of $\theta$ decreases towards zero as $\beta$ is taken to infinity.Comment: 3 pages, DESY 93-177, talk presented by G. Schierholz at Lattice9

A Proposal for Simulating Chiral Fermions

We describe a method for evaluating chiral gauge theories that is not plagued by the doubling problem. To demonstrate the efficiency of the approach, we apply our ideas to the chiral Schwinger model.Comment: 10 pages, HLRZ 92-3

The QCD axion beyond the classical level: A lattice study

The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory to resolve the strong CP problem in QCD. If axions exist and have low mass, they are a candidate for dark matter as well. So far our knowledge of the properties of the QCD axion rests on semi-classical arguments and effective theory. In this work we perform, for the first time, a fully dynamical investigation of the Peccei-Quinn theory, focussing on the axion mass, by simulating the theory on the lattice. The results of the simulation are found to be in conflict with present axion phenomenology.Comment: 16 pages, 9 figures; theoretical considerations refined, numerical results on larger lattices added, text corrected and improve

On the structure of the Yang-Mills vacuum

In this talk I will discuss the current picture of color confinement. In particular, I will show how it can be tested microscopically. It is stressed that the color magnetic monopoles in this picture are dyons. Furthermore, the role of instantons is illuminated

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

Feynman-Hellmann theorem for resonances and the quest for QCD exotica

The generalization of the Feynman-Hellmann theorem for resonance states in quantum field theory is derived. On the basis of this theorem, a criterion is proposed to study the possible exotic nature of certain hadronic states emerging in QCD. It is shown that this proposal is supported by explicit calculations in Chiral Perturbation Theory and by large-$N_c$ arguments. Analyzing recent lattice data on the quark mass dependence in the pseudoscalar, vector meson, baryon octet and baryon decuplet sectors, we conclude that, as expected, these are predominately quark-model states, albeit the corrections are non-negligible.Comment: 26 pages, 2 figure