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John W. Negele

Publications and source records attributed to John W. Negele.

32 records · Page 2Linked to original sources
arXiv2007

Electromagnetic form factors of the Delta baryon

We develop a methodology that enables us to extract accurately the electromagnetic Delta form factors and their momentum dependence. We test our approach in the quenched approximation as a preparation for a study using dynamical fermions. Our calculation of the four form factors covers pion masses between about 410 MeV and 560 MeV on lattices with a size of 2.9 fm and a lattice spacing 0.09 fm. From the form factors we are able to obtain estimates of the magnetic moment and the charge radius of the Delta, which we compare to existing experimental and theoretical results.Our non-zero result for the electric quadrupole form factor signals a deformation of the Delta, pointing to an oblate charge distribution.

hep-lat↗
arXiv2007

Oscillatory terms in the domain wall transfer matrix

We study the transfer matrix for domain wall fermions to understand the origin and significance of oscillatory contributions to hadron correlation functions that arise for M >1. For a free particle in one space, one time, and one flavor dimension, the eigenmodes of the one-body operator appearing in the transfer matrix are calculated, and the role of the negative eigenmodes arising when M > 1 is studied. In the case of three space dimensions, oscillatory behavior for hadron correlation functions in QCD is shown to emerge for free fermions when M exceeds 1, and to increase with increasing M. Analogous behavior is observed for domain wall fermions on HYP smeared MILC lattices, and a procedure is demonstrated for subtracting oscillating terms from physical observables.

hep-lat↗
arXiv2007

The Glue Content of the Pion

We perform a quenched computation of the glue momentum fraction in the pion. Different discretizations of the gluonic energy-momentum tensor are studied on the lattice for that purpose. We discuss some implications based on the momentum sum rule. Finally we point out promising applications of the techniques developed here.

hep-lat↗
arXiv2007

Gluon contributions to the pion mass and light cone momentum fraction

We calculate the matrix elements of the gluonic contributions to the energy-momentum tensor for a pion of mass 600 < Mpi < 1100 MeV in quenched lattice QCD. We find that gluons contribute (37 +/- 8 +/- 12)% of the pion's light cone momentum. The bare matrix elements corresponding to the trace anomaly contribution to the pion mass are also obtained. The discretizations of the energy-momentum tensor we use have other promising applications, ranging from calculating the origin of hadron spin to QCD thermodynamics.

hep-lat↗
arXiv2007

The N to $Δ$ axial transition form factors in quenched and unquenched QCD

The four N to $Δ$ axial transition form factors are evaluated using quenched QCD, using two flavors of dynamical Wilson fermions and using domain wall valence fermions on three-flavor MILC configurations for pion masses down to 360 MeV. We provide a prediction for the parity violating asymmetry as a function of $Q^2$ and examine the validity of the non-diagonal Goldberger-Treiman relation.

hep-lat↗
arXiv2005

A study of the N to Delta transition form factors in full QCD

The N to Delta transition form factors GM1, GE2 and GC2 are evaluated using dynamical MILC configurations and valence domain wall fermions at three values of quark mass corresponding to pion mass 606 MeV, 502 MeV and 364 MeV on lattices of spatial size $20^3$ and $28^3$. The unquenched results are compared to those obtained at similar pion mass in the quenched theory.

hep-lat↗
arXiv2005

Hadron structure with light dynamical quarks

Generalized parton distributions encompass a wealth of information concerning the three-dimensional quark and gluon structure of the nucleon, and thus provide an ideal focus for the study of hadron structure using lattice QCD. The special limits corresponding to form factors and parton distributions are well explored experimentally, providing clear tests of lattice calculations, and the lack of experimental data for more general cases provides opportunities for genuine predictions and for guiding experiment. We present results from hybrid calculations with improved staggered (Asqtad) sea quarks and domain wall valence quarks at pion masses down to 350 MeV.

hep-lat↗
arXiv2002

Monopole and vortex content of a meron pair

We investigate the monopole and vortex content of a meron pair by calculating the points at which the transformation to the Laplacian Center Gauge is ill-defined and by studying the behavior of Wilson loops. These techniques reveal complementary aspects of the vortex and monopole structure, including the presence of closed monopole lines and closed vortex surfaces joining the two merons, and evidence for intersecting vortex surfaces at each meron.

hep-lat↗
arXiv2000

Meron Pairs and Fermion Zero Modes

Merons, conjectured as a semiclassical mechanism for color confinement in QCD, have been described analytically by either infinite action configurations or an Ansatz with discontinuous action. We construct a smooth, finite action, stationary lattice solution corresponding to a meron pair. We also derive an analytical solution for the zero mode of the meron pair Ansatz, show that it has the qualitative behavior of the exact zero mode of the lattice solution, and propose the use of zero modes to identify meron gauge field configurations in stochastic evaluations of the lattice QCD path integral.

hep-lat↗
arXiv2000

Phases and Residual Gauge Symmetries of Higgs Models

After elimination of the redundant variables, gauge theories may still exhibit symmetries associated with the gauge fields. The role of these residual gauge symmetries is discussed within the Abelian Higgs model and the Georgi-Glashow model. In the different phases of these models, these symmetries are realized differently. The characteristics of emergence and disappearance of the symmetries are studied in detail and the implications for the dynamics in Coulomb, Higgs, and confining phases are discussed.

hep-th↗
arXiv2000

Instanton and Meron Physics in Lattice QCD

Lattice field theory provides a quantitative tool to study the role of nonperturbative semiclassical configurations in QCD. This talk briefly reviews our present understanding of the role of instantons in QCD and describes in detail new developments in the study of merons on the lattice.

hep-lat↗
arXiv1998

Instantons, the QCD Vacuum, and Hadronic Physics

A large body of evidence from lattice calculations indicates that instantons play a major role in the physics of light hadrons. This evidence is summarized, and recent results concerning the instanton content of the SU(3) vacuum, instanton contributions to the static potential, and a new class of instanton solutions at finite temperature are reviewed.

hep-lat↗