The fixed point action of the Schwinger model

We compute the fixed point action for the Schwinger model through an expansion in the gauge field. The calculation allows a check of the locality of the action. We test its perfection by computing the 1-loop mass gap at finite spatial volume.Comment: 3 pages, LaTeX, 2 figures, uses styles [twoside,fleqn,espcrc2, epsfig], talk presented at Lattice 9

Partially quenched chiral perturbation theory and numerical simulations

The dependence of the pseudoscalar meson mass and decay constant is compared to one-loop Partially Quenched Chiral Perturbation Theory (PQChPT) in a numerical simulation with two light dynamical quarks. The characteristic behaviour with chiral logarithms is observed. The values of the fitted PQChPT-parameters are in a range close to the expectation in continuum in spite of the fact that the lattice spacing is still large, namely a=0.28 fm.Comment: 11 pages, 3 figures; discussion of the results in section 3 extende

Wilson, fixed point and Neuberger's lattice Dirac operator for the Schwinger model

We perform a comparison between different lattice regularizations of the Dirac operator for massless fermions in the framework of the single and two flavor Schwinger model. We consider a) the Wilson-Dirac operator at the critical value of the hopping parameter; b) Neuberger's overlap operator; c) the fixed point operator. We test chiral properties of the spectrum, dispersion relations and rotational invariance of the mesonic bound state propagators.Comment: Revised version; 13 pages (LaTeX), 3 figures (EPS

The Volume Source Technique for flavor singlets: a second look

We reconsider the Volume Source Technique (VST) for the determination of flavor singlet quantities on the lattice. We point out a difficulty arising in the case of fermions in real representations of the gauge group and propose an improved version of the method (IVST) based on random gauge transformations of the background configuration. We compare the performance of IVST with the method based on stochastic estimators (SET). We consider the case of the N=1 Supersymmetric Yang-Mills Theory (SYM), where just one fermionic flavor is present, the gluino in the adjoint representation, and only flavor singlet states are possible. The work is part of an inclusive analysis of the spectrum of the lightest particles of the theory, based on the simulation of the model on a $16^3\cdot32$ lattice with dynamical gluinos in the Wilson scheme.Comment: 11 pages, 6 figures, some formulations change

Masses and Decay Constants of Pseudoscalar Mesons to Two Loops in Two-Flavor Partially Quenched Chiral Perturbation Theory

This paper presents a first study of the masses and decay constants of the charged, or flavor-off-diagonal, pseudoscalar mesons to two loops for two flavors of sea-quarks, in Partially Quenched Chiral Perturbation Theory (PQ$\chi$PT). Explicit analytical expressions up to ${\cal O}(p^6)$ in the momentum expansion are given. The calculations have been performed within the supersymmetric formulation of PQ$\chi$PT. A numerical analysis is done to indicate the size of the corrections.Comment: 20 pages, subsection about determining the LECs from lattice results added, v3 one misprint correcte

Lattice Spacing Dependence of the First Order Phase Transition for Dynamical Twisted Mass Fermions

Lattice QCD with Wilson fermions generically shows the phenomenon of a first order phase transition. We study the phase structure of lattice QCD using Wilson twisted mass fermions and the Wilson plaquette gauge action are used in a range of beta values where such a first order phase transition is observed. In particular, we investigate the dependence of the first order phase transition on the value of the lattice spacing. Using only data in one phase and neglecting possible problems arising from the phase transition we are able to perform a first scaling test for physical quantities using this action.Comment: 15 pages, 7 figures, typo corrected, web-list of authors correcte

Lattice QCD with light dynamical quarks

We report on the simulation of QCD with light dynamical quarks using the two-step multi-boson (TSMB) algorithm. In an exploratory study with two flavours of quarks at lattice spacing about 0.27 fm and with quark mass down to one sixth of the strange quark mass eigenvalue spectra and autocorrelations have been studied. Here we present results on the volume dependence as well as tests of possible algorithmic improvements.Comment: 6 pages, Lattice2002(spectrum