George T. Fleming

Nucleon Axial Charge in Full Lattice QCD

The nucleon axial charge is calculated as a function of the pion mass in full QCD. Using domain wall valence quarks and improved staggered sea quarks, we present the first calculation with pion masses as light as 354 MeV and volumes as large as (3.5 fm)3. We show that finite volume effects are small for our volumes and that a constrained fit based on finite volume chiral perturbation theory agrees with experiment within 7% statistical errors.

Insight into nucleon structure from lattice calculations of moments of parton and generalized parton distributions

Abstract This talk presents recent calculations in full QCD of the lowest three moments of generalized parton distributions and the insight they provide into the behavior of nucleon electromagnetic form factors, the origin of the nucleon spin, and the transverse structure of the nucleon. In addition, new exploratory calculations in the chiral regime of full QCD are discussed.

Hadronic physics with domain-wall valence and improved staggered sea quarks

With the advent of chiral fermion formulations, the simulation of light valence quarks has finally become realistic for numerical simulations of lattice QCD. The simulation of light dynamical quarks, however, remains one of the major challenges and is still an obstacle to realistic simulations. We attempt to meet this challenge using a hybrid combination of Asqtad sea quarks and domain-wall valence quarks. Initial results for the proton form factor and the nucleon axial coupling are presented.

Moments of nucleon spin-dependent generalized parton distributions

Abstract We present a lattice measurement of the first two moments of the spin-dependent GPD H ∼~ (x, ξ, t) . From these we obtain the axial coupling constant and the second moment of the spin-dependent forward parton distribution. The measurements are done in full QCD using Wilson fermions. In addition, we also present results from a first exploratory study of full QCD using Asqtad sea and domain-wall valence fermions.

Baryonic operators for lattice simulations

Abstract The construction of baryonic operators for determining the N ∗ excitation spectrum is discussed. The operators designed with one eye towards maximizing overlaps with the low-lying states of interest, and the other eye towards minimizing the number of sources needed in computing the required quark propagators. Issues related to spin identification are outlined. Although we focus on tri-quark baryon operators, the construction method is applicable to both mesons and penta-quark operators.

Baryon operators and spectroscopy in lattice QCD

Abstract The construction of the operators and correlators required to determine the excited baryon spectrum is presented, with the aim of exploring the spatial and spin structure of the states while minimizing the number of propagator inversions. The method used to construct operators that transform irreducibly under the symmetries of the lattice is detailed, and the properties of example operators is studied using domain-wall fermion valence propagators computed on MILL asqtad dynamical lattices.

What can Lattice QCD theorists learn from NMR spectroscopists

The Lattice QCD (LQCD) community has occasionally gone through periods of self-examination of its data analysis methods and compared them with methods used in other disciplines [22, 16, 18]. This process has shown that the techniques widely used elsewhere may also be useful in analyzing LQCD data. It seems that we are in such a period now with many groups trying what are generally called Bayesian methods such as Maximal Entropy (MEM) or constrained fitting [19, 15, 1, 7, 5, and many others]. In these proceedings we will attempt to apply this process to a comparison of data modeling techniques used in LQCD and NMR Spectroscopy to see if there are methods which may also be useful when applied to LQCD data.

Mesonic Form Factors

Abstract We have started a program to compute the electromagnetic form factors of mesons. We discuss the techniques used to compute the pion form factor and present preliminary results computed with domain wall valence fermions on MILC asqtad lattices, as well as Wilson fermions on quenched lattices. These methods can easily be extended to ϱ → γπ transition form factors.

Nucleon form factors from high statistics mixed-action calculations with 2+1 flavors

We present new high-statistics results for nucleon form factors at pion masses of approximately 290, 350, 500, and 600 MeV using a mixed action of domain wall valence quarks on an improved staggered sea. We perform chiral fits to both vector and axial form factors and compare our results to experiment.

Lattice study of ChPT beyond QCD

Thomas Appelquista, Adam Avakianb, Ron Babichb, Richard C. Browerb, Michael Chengc, Michael A. Clark f g, Saul D. Cohenb, George T. Fleminga, Joseph Kiskisd , Ethan T. Neil∗a, James C. Osborne, Claudio Rebbib, David Schaichb, Pavlos Vranasc a Department of Physics, Sloane Laboratory, Yale University, New Haven, CT 06520 b Department of Physics, Boston University, Boston, MA 02215 c Physical Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA