728 research outputs found

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

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    We examine the phase structure of the CP3CP^3 model as a function of θ\theta in the weak coupling regime. It is shown that the model has a first order phase transition at small θ\theta. We pay special attention to the extrapolation of the data to the infinite volume. It is found that the critical value of θ\theta decreases towards zero as β\beta is taken to infinity.Comment: 3 pages, DESY 93-177, talk presented by G. Schierholz at Lattice9

    A Proposal for Simulating Chiral Fermions

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    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

    On the structure of the Yang-Mills vacuum

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    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

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

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    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-NcN_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

    Effective Yukawa Couplings in Noncompact Lattice QED

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    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

    The pi-N Sigma term - a lattice investigation

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    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

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    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
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