Searching for dynamical fermion effects in UKQCD simulations

We present recent results from the UKQCD collaboration's dynamical QCD simulations. This data has fixed lattice spacing but varying dynamical quark mass. We concentrate on searching for an unquenching signal in the mesonic mass spectrum where we do not find a significant effect at the quark masses considered.Comment: 3 pages, 3 figures, Lattice2001(spectrum

Lattice QCD with Dynamical Quarks from the UKQCD Collaboration

A brief overview of the lattice technique of studying QCD is presented. Recent results from the UKQCD Collaboration's simulations with dynamical quarks are then presented. In this work, the calculations are all at a fixed lattice spacing and volume, but varying sea quark mass from infinite (corresponding to the quenched simulation) down to roughly that of the strange quark mass. The main aim of this work is to uncover dynamical quark effects from these ``matched'' ensembles.Comment: Invited paper presented at the International Light-Cone Workshop "Light-cone Physics: Particles and Strings", September 2001, Trento, Italy. 7 page

Recent Results from (Full) Lattice QCD

An overview of the Lattice technique for studies of the strong interaction is given. Recent results from the UKQCD lattice collaboration are presented. These concentrate on spectral quantities calculated using full (i.e. unquenched) QCD. A comparison with quenched results is made. Novel methods of extracting spectral properties from two-point functions are described.Comment: Invited Review Talk at "Workshop on Light-Cone QCD and Nonperturbative Hadron Physics", December 1999, Adelaide, Australia. To be published in the proceedings (World Scientific). 10 pages latex, including 5 ps figure

Study of Lattice Correlation Functions at Small Times using the QCD Sum Rules Continuum Model

In this paper we study the work of Leinweber by applying the Continuum Model of QCD Sum Rules (QCDSR) to the analysis of (quenched) lattice correlation functions. We expand upon his work in several areas: we study meson states as well as baryons; we analyse data from several lattice spacings; and we include data from the Sheikholeslami-Wohlert (clover) improved action. We find that the QCDSR Continuum Model Ansatz can reproduce the data, but only for non-physical values of its parameters. This leads us to reject it as a model for hadronic correlation functions. We study the non-relativistic quark model and conclude that it predicts essentially the same form for the correlation function as the QCDSR Continuum Model approach. Furthermore, because it doesn't have the Continuum Model's restrictions on the parameters, the non-relativistic quark model can be viewed as a successful Ansatz. As well as studying the validity or otherwise of the QCDSR Continuum Model approach, this paper defines 4-parameter fitting functions that can be used to fit lattice data even for a time window close to the source. These functions are shown to be an improvement over 2-exponential fits especially in the case of mesons. We encourage the application of this approach to situations where the conventional fitting procedures are problematic due to poor ground state dominance.Comment: 33 pages, uses elsart.sty (included), 10 postscript figure

Recent Lattice QCD Results from the UKQCD Collaboration

The lattice technique of studying the strong interaction of matter is used to obtain predictions of the hadronic spectrum. These simulations were performed by the UKQCD collaboration using full (unquenched) QCD. Details of the results, a comparison with quenched data, and novel methods of extracting spectral properties are described.Comment: Paper presented at the Computational Physics Conference CCP2000, 3-8 Decmeber 2000, Gold Coast, Australia, 5 pages, 3 figure

Effects of Dynamical Quarks in UKQCD Simulations

Recent results from the UKQCD Collaboration's dynamical simulations are presented. The main feature of these ensembles is that they have a fixed lattice spacing and volume, but varying sea quark mass from infinite (corresponding to the quenched simulation) down to roughly that of the strange quark mass. The main aim of this work is to uncover dynamical quark effects from these ``matched'' ensembles. We obtain some evidence of dynamical quark effects in the static quark potential with less effects in the hadronic spectrum.Comment: Invited paper presented at the Workshop on Lattice Hadron Physics, July 2001, Cairns, Australia. 7 pages. Uses espcrc2.sty (included

QCD Sum Rules on the Lattice

We study the work of Leinweber by applying the Continuum Model of QCD Sum Rules (QCDSR) to the analysis of (quenched) lattice correlation functions. We expand upon his work in several areas and find that, while the QCDSR Continuum Model very adequately fits lattice data, it does so only for non-physical values of its parameters. The non-relativistic model is found to predict essentially the same form for the correlation functions as the QCDSR Continuum Model but without the latter's restrictions. By fitting lattice data to a general form which includes the non-relativistic quark model as a special case, we confirm it as the model of choice.Comment: Talk presented by C.R. Allton at LAT97, Edinburgh. 3 pages, uses espcrc2.st

Spectral Functions, Maximum Entropy Method and Unconventional Methods in Lattice Field Theory

We present two unconventional methods of extracting information from hadronic 2-point functions produced by Monte Carlo simulations. The first is an extension of earlier work by Leinweber which combines a QCD Sum Rule approach with lattice data. The second uses the Maximum Entropy Method to invert the 2-point data to obtain estimates of the spectral function. The first approach is applied to QCD data, and the second method is applied to the Nambu--Jona-Lasinio model in (2+1)D. Both methods promise to augment the current approach where physical quantities are extracted by fitting to pure exponentials.Comment: Paper presented at the Workshop on Lattice Hadron Physics, July 2001, Cairns, Australia. 5 pages. Minor spelling error correcte

Lattice Monte Carlo Data versus Perturbation Theory

Differences between lattice Monte Carlo data and perturbation theory (for example the lack of asymptotic scaling) are usually associated with the `bad' behaviour of the bare lattice coupling g_0 due to the effects of large (and unknown) higher order terms in g_0. In this philosophy a new, renormalised coupling g' is defined with the aim of making the higher order coefficients of the perturbative series in g' as small as possible. In this paper an alternative scenario is discussed where lattice artifacts are proposed as the cause of the disagreement between Monte Carlo data and the g_0-perturbative series. We find that with the addition of a lattice artifact term, the usual asymptotic scaling expression in g_0 is in excellent agreement with Monte Carlo data. Lattice data studied includes the string tension, the hadronic scale r_0, the discrete beta function, M_rho, f_pi and the 1P-1S splitting in charmonium.Comment: 3 pages, LaTeX. Uses espcrc2.sty and fleqn.sty (included) Talk presented at LATTICE96(improvement