The Nambu-Jona-Lasinio model with staggered fermions

We investigate the neighbourhood of the chiral phase transition in a lattice Nambu--Jona-Lasinio model, using both Monte Carlo methods and lattice Schwinger-Dyson equations.Comment: Talks at LAT93, Dallas, U.S.A. Postscript file, 6 pages, figures include

Resolution of the Landau pole problem in QED

We present new numerical results for the renormalized mass and coupling in non-compact lattice QED with staggered fermions. Implications for the continuum limit and the role of the Landau pole are discussed.Comment: 3 pages, talk presented by H. St\"uben at Lattice '97, Edinburg

Baryonic Flux in Quenched and Two-Flavor Dynamical QCD after Abelian projection

We study the distribution of color electric flux of the three-quark system in quenched and full QCD (with N_f = 2 flavors of dynamical quarks) at zero and finite temperature. To reduce ultra-violet fluctuations, the calculations are done in the abelian projected theory fixed to the maximally abelian gauge. In the confined phase we find clear evidence for a Y--shape flux tube surrounded and formed by the solenoidal monopole current, in accordance with the dual superconductor picture of confinement. In the deconfined, high temperature phase monopoles cease to condense, and the distribution of the color electric field becomes Coulomb--like.Comment: 21 pages, 15 figures, Latex, published version (4 figures added

The present status of non-compact lattice QED

We give a 1993 update of non-compact lattice QED, in particular the chiral condensate, finite size effects and meson mass ratios. We compare descriptions of the phase transition. Our previous conclusions remain valid.Comment: Poster presentation at LAT93, Dallas, U.S.A. Postscript file, 4 pages, figures included. Preprint numbers DESY-93-178, FUB-HEP/93-20 and HLRZ 93-7

Profiles of the broken string in two-flavor QCD below and above the finite temperature transition

We study the Abelian flux tube profile of mesonic and the baryonic configurations of static quarks below and above the finite-temperature transition in $N_f=2$ full QCD. To reduce effects of ultra-violet fluctuations we measure Abelian distributions of the action density, the color-electric field and the monopole current after fixing to the maximally Abelian gauge. Changing the distance $R$ between quarks for fixed $T/T_c<1$, one can see a clear signal of string breaking for large $R$. The electric field becomes Coulomb-like and the circulating monopole current disappears. We study also the temperature dependence of the flux profile for fixed $R \approx 0.7$ fm. The disappearance of the squeezed flux is observed clearly above $T_c$. Similar behaviors are observed both in the mesonic and the baryonic systems.Comment: 17 pages, 13 figures, Late

Meson decay constants from Nf=2 clover fermions

We present recent results for meson decay constants calculated on configurations with two flavours of O(a)-improved Wilson fermions. Non-perturbative renormalisation is applied and quark mass dependencies as well as finite volume and discretisation effects are investigated. In this work we also present a computation of the coupling of the light vector mesons to the tensor current using dynamical fermions.Comment: 6 pages, contribution to Lattice2005(Hadron spectrum and quark masses

A determination of the strange quark mass for unquenched clover fermions using the AWI

Using the O(a) Symanzik improved action an estimate is given for the strange quark mass for unquenched (nf=2) QCD. The determination is via the axial Ward identity (AWI) and includes a non-perturbative evaluation of the renormalisation constant. Numerical results have been obtained at several lattice spacings, enabling the continuum limit to be taken. Results indicate a value for the strange quark mass (in the MSbar-scheme at a scale of 2GeV) in the range 100 - 130MeV.Comment: 6 pages, contribution to Lattice2005(Hadron spectrum and quark masses), uses PoS.cl

Progress towards a lattice determination of (moments of) nucleon structure functions

Using unimproved and non-perturbatively O(a) improved Wilson fermions, results are given for the three lowest moments of unpolarised nucleon structure functions. Renormalisation, chiral extrapolation and the continuum limit of the matrix elements are briefly discussed. The simulations are performed for both quenched and two flavours of unquenched fermions. No obvious sign of deviation from linearity in the chiral extrapolations are found. (This is most clearly seen in our quenched unimproved data, which extends to lighter quark mass.) Possible quenching effects also seem to be small. The lowest moment thus remains too large, so it seems to be necessary to reach smaller quark masses in numerical simulations.Comment: 3 pages, Latex, 4 figures, Talk presented at Lattice2001(matrixelement

Accelerating Hasenbusch's acceleration of Hybrid Monte Carlo

Hasenbusch has proposed splitting the pseudo-fermionic action into two parts, in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a different splitting, also using clover-improved Wilson fermions. An additional speed-up between 5 and 20% over the original proposal was achieved in production runs.Comment: Poster presented by H. Stueben at Lattice2003, meta-data correcte

A Determination of the Lambda Parameter from Full Lattice QCD

We present a determination of the QCD parameter Lambda in the quenched approximation (n_f=0) and for two flavours (n_f=2) of light dynamical quarks. The calculations are performed on the lattice using O(a) improved Wilson fermions and include taking the continuum limit. We find Lambda_{n_f=0} = 259(1)(20) MeV and Lambda_{n_f=2} = 261(17)(26) MeV}, using r_0 = 0.467 fm to set the scale. Extrapolating our results to five flavours, we obtain for the running coupling constant at the mass of the Z boson alpha_s(m_Z) = 0.112(1)(2). All numbers refer to the MSbar scheme.Comment: 25 pages, 9 figure