First results in QCD with 2+1 light flavors using the fixed-point action

This is a progress report on 2+1 flavor simulation with the FP action on a lattice with spatial size L=1.2fm. Since m_{ud} is quite small in our simulation we are in the delta regime for the two light flavors where the low lying excitations are described by a quantum mechanical rotator. From here we extract the low energy constant F. We also measure the AWI mass and present results on numerical issues like low-mode averaging and autocorrelation times.Comment: 7 pages, 6 figures, parallel talk at LATTICE 200

The Exotic Baryon Theta^+(1540) on the Lattice

We report on a study of the pentaquark Theta^+(1540), using a variety of different interpolating fields. We use Chirally Improved fermions in combination with Jacobi smeared quark sources to improve the signal and get reliable results even for small quark masses. The results of our quenched calculations, which have been done on a 12^3x24 lattice with a lattice spacing of a=0.148 fm, do not provide any evidence for the existence of a Theta^+ with positive parity. We do observe, however, a signal compatible with nucleon-kaon scattering state. For the negative parity the results are inconclusive, due to the potential mixture with nucleon-kaon and N*-kaon scattering states.Comment: 6 pages, 1 figure, Proceedings of "Lattice 2005" (Dublin, 25-30 July 2005

2+1 flavor QCD with the fixed point action in the ϵ\epsilon-regime

We generated configurations with the approximate fixed-point Dirac operator $D_\mathrm{FP}$ on a $12^4$ lattice with $a \approx 0.13$fm where the scale was set by $r_0$. The distributions of the low lying eigenvalues in different topological sectors were compared with those of the Random Matrix Theory which leads to a prediction of the chiral condensate.Comment: 6 pages, 5 figures, presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German

Baryon spectroscopy with spatially improved quark sources

We study baryons on the lattice with a special focus on excited states. For that purpose we construct several interpolators which differ in their Dirac structure. These interpolators are built from Jacobi smeared quarks with different widths in order to allow for operators with improved spatial wavefunctions. We compute all cross correlations and use the variational method to determine which combinations of operators have best overlap with ground and excited states. Our approach yields promising results for the spin-1/2 baryons: nucleon, sigma, xi and lambda. For the spin-3/2 baryons, delta and omega, we obtain results which are consistent with results of other groups.Comment: LaTeX [PoS], 6 pages, 4 figures, talk presented at Lattice 2005 (Hadron spectrum and quark masses

Masses of excited baryons from chirally improved quenched lattice QCD

Whereas ground state spectroscopy for quenched QCD is well understood, it is still a challenge to obtain results for excited hadron states. In our study we present results from a new approach for determining spatially optimized operators for lattice spectroscopy of excited hadrons. In order to be able to approach physical quark masses we work with the chirally improved Dirac operator, i.e., approximate Ginsparg-Wilson fermions. Since these are computationally expensive we restrict ourselves to a few quark sources. We use Jacobi smeared quark sources with different widths and combine them to construct hadron operators with different spatial wave functions. This allows us to identify the Roper state and other excited baryons, also in the strange sector.Comment: Contribution to BARYONS 2004, Palaiseau, France, October 25 - 29, 2004; 4 pages, 1 figure, Style espcrc

Lattice Quantum ChromoDynamics with approximately chiral fermions

In this work we present Lattice QCD results obtained by approximately chiral fermions. We use the CI fermions in the quenched approximation to investigate the excited baryon spectrum and to search for the Theta^+ pentaquark on the lattice. Furthermore we developed an algorithm for dynamical simulations using the FP action. Using FP fermions we calculate some LECs of chiral perturbation theory applying the epsilon expansion

Excited meson spectroscopy with chirally improved fermions

We present excited meson masses from quenched calculations using chirally improved (CI) quarks at pion masses down to 350 MeV. The salient features of our analysis are the use of a matrix of correlators from various source and sink operators and a basis which includes quark sources with different spatial widths, thereby improving overlap with states exhibiting radial excitations