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In a recent paper [1] we presented precise lattice QCD results of our European Twisted Mass Collaboration (ETMC). They were obtained by employing two mass-degenerate flavours of twisted mass fermions at maximal twist. In the present paper we give details on our simulations and the computation of physical observables. In particular, we discuss the problem of(More)
The effect of changing the lattice action for the gluon field on the recently observed [1] first order phase transition near zero quark mass is investigated by replacing the Wilson plaquette action by the DBW2 action. The lattice action for quarks is unchanged: it is in both cases the original Wilson action. It turns out that Wilson fermions with the DBW2(More)
X iv :h ep -l at /0 40 91 09 v1 1 7 Se p 20 04 Comparison between overlap and twisted mass fermions towards the chiral limit χLF Coll.: W. Bietenholz , S. Capitani, T. Chiarappa, M. Hasenbusch, K. Jansen, K.-I. Nagai, M. Papinutto, L. Scorzato, S. Shcheredin, A. Shindler, C. Urbach, U. Wenger , I. Wetzorke. Humboldt Universität zu Berlin, Institut für(More)
We carry out an exploratory study of the isospin one a0(980) and the isospin one-half κ scalar mesons using Nf = 2 + 1 + 1 Wilson twisted mass fermions at one lattice spacing. The valence strange quark is included as an Osterwalder-Seiler fermion with mass tuned so that the kaon mass matches the corresponding mass in the unitary Nf = 2+1+1 theory. We(More)
In the framework of Wilson Chiral Perturbation Theory [1], we study the effect induced by a twisted Wilson term, as it appears in Twisted Mass QCD [2] (with 2 degenerate quarks). In particular we consider the vacuum orientation and the pion masses. The computations are done to NLO both in the mass and in the lattice spacing (i.e. to O(a)). There are no(More)
We identify the global symmetries of SU(2) lattice gauge theory with N flavors of staggered fermion in the presence of a quark chemical potential μ, for fermions in both fundamental and adjoint representations, and anticipate likely patterns of symmetry breaking at both low and high densities. Results from numerical simulations of the model with N = 1(More)
We present an update on Numerical Stochastic Perturbation Theory projects for Lattice QCD, which are by now run on apeNEXT. As a first issue, we discuss a strategy to tackle finite size effects which can be quite sizeable in the computation of logarithmically divergent renormalization constants. Our first high loop determination of quark bilinears for(More)
1 Goethe-Universität Frankfurt am Main, Institut für Theoretische Physik, Max-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany 2 Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus 3 Computation-based Science and Technology Research Center, Cyprus Institute, 20 Kavafi Str., Nicosia 2121, Cyprus 4 Helmholtz-Institut für(More)
We study the light scalar mesons a0(980) and κ using N f = 2+ 1+ 1 flavor lattice QCD. In order to probe the internal structure of these scalar mesons, and in particular to identify, whether a sizeable tetraquark component is present, we use a large set of operators, including diquarkantidiquark, mesonic molecule and two-meson operators. The inclusion of(More)