Low-mode averaging for baryon correlation functions

The low-mode averaging technique is a powerful tool for reducing large fluctuations in correlation functions due to low-mode eigenvalues of the Dirac operator. In this work we propose a generalization to baryons and test our method on two-point correlation functions of left-handed nucleons, computed with quenched Neuberger fermions on a lattice with extension L=1.5 fm. We show that the statistical fluctuations can be reduced and the baryon signal significantly improved.Comment: 6 pages, talk presented at the XXIIIrd International Symposium on Lattice Field Theory, 25-30 July 2005, Trinity College, Dublin, Irelan

Wilson fermions in the epsilon regime

We extend the epsilon-expansion of continuum chiral perturbation theory to nonzero lattice spacing in the framework of Wilson Chiral Perturbation Theory. We distinguish various regimes by defining the relative power counting of the quark mass m and the lattice spacing a. We observe that for m ~ a Lambda^2_QCD, the explicit breaking of chiral symmetry in Wilson fermions is still driven by the quark mass and lattice corrections are highly suppressed. The lattice spacing effects become more pronounced for smaller quark masses and may lead to non-trivial corrections of the continuum results at next-to-leading order. We compute these corrections for standard current and density correlation functions. A fit to lattice data shows that these corrections are small, as expected.Comment: Talk presented at the XXVII International Symposium on Lattice Field Theory, July 26-31, 2009, Peking University, Beijing, China; 7 pages, 1 figur

Finite-size scaling of heavy-light mesons

We study the finite-size scaling of heavy-light mesons in the static limit. The most relevant effects are due to the pseudo-Goldstone boson cloud. In the HMChPT framework we compute two-point functions of left current densitities as well as pseudoscalar densitites for the cases in which some or all of them lay in the epsilon-regime. As expected, finite volume dependence turns out to be significant in this regime and can be predicted in the effective theory in terms of the infinite-volume low-energy couplings. These results might be relevant for extraction of heavy-light meson properties from lattice simulations.Comment: 7 pages, 2 figures, Contributed to 27th International Symposium on Lattice Field Theory, Beijing, China, 26 - 31 Jul 200

The epsilon regime with Wilson fermions

We study the impact of explicit chiral symmetry breaking of Wilson fermions on mesonic correlators in the epsilon-regime using Wilson chiral perturbation theory (WChPT). We generalize the epsilon-expansion of continuum ChPT to nonzero lattice spacings for various quark mass regimes. It turns out that the corrections due to a nonzero lattice spacing are highly suppressed for typical quark masses of the order aLambda_QCD^2. The lattice spacing effects become more pronounced for smaller quark masses and lead to non-trivial corrections of the continuum ChPT results at next-to-leading order. We compute these corrections for the standard current and density correlation functions. A fit to lattice data shows that these corrections are small, as expected.Comment: 29 pages, 2 figure

Chiral low-energy constants from lattice QCD

Different strategies for the computation of QCD low-energy couplings by matching lattice results with the chiral effective theory are reviewed. After recalling some relevant predictions from the effective theory, the current status of leading order (\Sigma,F, Sigma_0,F_0) and next-to-leading order (l_i, L_i) low-energy constants is summarized, focusing on recent results obtained with N_f=2 and N_f=2+1 lattice simulations.Comment: Plenary talk at 8th Conference Quark Confinement and the Hadron Spectrum, September 1-6 2008, Mainz (Germany

Exploring the epsilon regime with lattice Wilson fermions

We study the impact of explicit chiral symmetry breaking of lattice Wilson fermions on mesonic correlators in the epsilon-regime using Wilson chiral perturbation theory. We generalize the epsilon-expansion of continuum chiral perturbation theory to nonzero lattice spacing a and distinguish various regimes. It turnes out that lattice corrections are highly suppressed, as long as quark masses are of the order a\Lambda^2_QCD. The lattice spacing effects become more pronounced for smaller quark masses and may lead to non-trivial corrections of the continuum results at next-to-leading order. We compute these corrections for standard current and density correlation functions. A fit to lattice data shows that these corrections are small, as expected.Comment: 8 pages, 1 figure. Presented at the International Workshop on Effective Field Theories: from the pion to the upsilon, February 2-6 2009, Valencia, Spai

Electroweak penguins and SUSY K^0-\bar K^0 mixing with Neuberger quarks

We present results for Delta I=3/2 and Delta S=2 matrix elements relevant for CP violation in K->Pi Pi decays and for the K_S-K_L mass difference in the standard model and beyond. They were obtained with Neuberger fermions on quenched gauge configurations generated with the Wilson plaquette action at beta=6.0 on an 18^3x64 lattice.Comment: 4 LaTeX pages (espcrc2.sty), 6 figures. Combined contributions by J.H., L.L. and C.R. at Lattice2004(weak), Fermilab, June 21-26, 200

Critical exponents for higher-representation sources in 3D SU(3) gauge theory from CFT

We establish an exact mapping between the multiplication table of the irreducible representations of SU(3) and the fusion algebra of the two-dimensional conformal field theory in the same universality class of 3D SU(3) gauge theory at the deconfining point. In this way the Svetitsky-Yaffe conjecture on the critical behaviour of Polyakov lines in the fundamental representation naturally extends to whatever representation one considers. As a consequence, the critical exponents of the correlators of these Polyakov lines are determined. Monte Carlo simulations with sources in the symmetric two-index representation, combined with finite-size scaling analysis, compare very favourably with these predictions.Comment: 15 pages, 2 figure