Hadron Electromagnetic Structure: Shedding Light on Models and their Mechanisms

Strange quark contributions to the proton magnetic moment are estimated from a consideration of baryon magnetic moment sum rules. The environment sensitivity of quark contributions to baryon moments is emphasized. Pion cloud contributions to proton charge radii are examined in the framework of Chiral Perturbation Theory. The absence of scalar-diquark clustering in the nucleon is discussed.Comment: Lattice '93 presentation. UU-File is a single postscript file of a 3 page manuscript including figures. Ohio State U. PP #93-112

Essential Strangeness in Nucleon Magnetic Moments

Effective quark magnetic moments are extracted from experimental measurements as a function of the strangeness magnetic moment of the nucleon. Assumptions made in even the most general quark model analyses are ruled out by this investigation. Ab initio QCD calculations demand a non-trivial role for strange quarks in the nucleon. The effective moments from QCD calculations are reproduced for a strangeness magnetic moment contribution to the proton of 0.11 $\mu_N$, which corresponds to $F_2^s(0) = -0.33\ \mu_N$.Comment: HYP '94 presentation. File is a uuencoded postscript file of a 2 page manuscript including figures. Also available via anonymous ftp from pacific.mps.ohio-state.edu in pub/NTG/Leinweber as StrQrkNmom.ps(.gz) OSU PP #94-063

Incorporating Chiral Symmetry in Extrapolations of Octet Baryon Magnetic Moments

We explore methods of extrapolating lattice calculations of hadronic observables to the physical regime, while respecting the constraints of chiral symmetry and heavy quark effective theory. In particular, we extrapolate lattice results for magnetic moments of the spin-1/2 baryon octet to the physical pion mass and compare with experimental measurements. The success previously reported for extrapolations of the nucleon magnetic moments carries over to the Sigma baryons. A study of the residual discrepancies in the Xi baryon moments suggests that it is important to have new simulation data with a more realistic strange quark mass.Comment: 9 pages, 4 figure

Electromagnetic Form Factors with FLIC fermions

The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a) improvement and allows efficient access to the light quark-mass regime. FLIC fermions enable the construction of the nonperturbatively O(a)-improved conserved vector current without the difficulties associated with the fine tuning of the improvement coefficients. The simulations are performed with an O(a^2) mean-field improved plaquette-plus-rectangle gluon action on a 20^3 x 40 lattice with a lattice spacing of 0.128 fm, enabling the first simulation of baryon form factors at light quark masses on a large volume lattice. Magnetic moments, electric charge radii and magnetic radii are extracted from these form factors, and show interesting chiral nonanalytic behavior in the light quark mass regime.Comment: Presented by J.Zanotti at the Workshop on Lattice Hadron Physics, Cairns, Australia, 2003. 7pp, 8 figure

Functional Forms for Lattice Correlators at Small Times

The analytic form of the lattice quark propagator is used to derive the functional form for short distance mesonic correlators. These are then used to calculate ``Continuum Model'' Ansatze which comprise of a pole, representing the ground state, plus a contribution for the excited states, coming from the short distance behaviour. These are compared to Monte Carlo data.Comment: 3 pages, 1 figure, Lattice2001(spectrum

Systematic uncertainties in the precise determination of the strangeness magnetic moment of the nucleon

Systematic uncertainties in the recent precise determination of the strangeness magnetic moment of the nucleon are identified and quantified. In summary, G_M^s = -0.046 \pm 0.019 \mu_N.Comment: Invited presentation at PAVI '04, International Workshop on Parity Violation and Hadronic Structure, Laboratoire de Physique Subatomique et de Cosmologie, Grenoble, France, June 8-11, 2004. 7 pages, 16 figure

Convergence of chiral effective field theory

We formulate the expansion for the mass of the nucleon as a function of pion mass within chiral perturbation theory using a number of different ultra-violet regularisation schemes; including dimensional regularisation and various finite-ranged regulators. Leading and next-to-leading order non-analytic contributions are included through the standard one-loop Feynman graphs. In addition to the physical nucleon mass, the expansion is constrained by recent, extremely accurate, lattice QCD data obtained with two flavors of dynamical quarks. The extent to which different regulators can describe the chiral expansion is examined, while varying the range of quark mass over which the expansions are matched. Renormalised chiral expansion parameters are recovered from each regularisation prescription and compared. We find that the finite-range regulators produce consistent, model-independent results over a wide range of quark mass sufficient to solve the chiral extrapolation problem in lattice QCD.Comment: 13 pages, 13 figures; To appear in Progress in Particle and Nuclear Physics; presented at Erice School on Quarks in Hadrons and Nuclei, September 200

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

Strangeness contributions to nucleon form factors

We review a recent theoretical determination of the strange quark content of the electromagnetic form factors of the nucleon. These are compared with a global analysis of current experimental measurements in parity-violating electron scattering.Comment: 5 pages, 6 figures; Talk presented at the International Workshop "From Parity Violation to Hadronic Structure and more...", Milos, Greece, May 16-20, 200

Chiral Nonanalytic Behaviour: The Edinburgh Plot

The Edinburgh Plot is a scale independent way of presenting lattice QCD calculations over a wide range of quark masses. In this sense it is appealing as an indicator of how the approach to physical quark masses is progressing. The difficulty remains that even the most state of the art calculations are still at quark masses that are too heavy to apply dimensionally-regulated chiral perturbation theory. We present a method allowing predictions of the behaviour of the Edinburgh plot, in both the continuum, and on the lattice.Comment: 3 pages, 4 figures, Lattice2002(Spectrum