3,594 research outputs found
Angular Momentum Decomposition for an Electron
We calculate the orbital angular momentum of the `quark' in the scalar
diquark model as well as that of the electron in QED (to order ). We
compare the orbital angular momentum obtained from the Jaffe-Manohar
decomposition to that obtained from the Ji relation and estimate the importance
of the vector potential in the definition of orbital angular momentum
Helicity Dependent and Independent Generalized Parton Distributions of the Nucleon in Lattice QCD
A complete description of the nucleon structure in terms of generalized
parton distributions (GPDs) at twist 2 level requires the
measurement/computation of the eight functions H, E, \tilde H, \tilde E, H_T,
E_T, \tilde H_T and \tilde E_T, all depending on the three variables x, \xi and
t. In this talk, we present and discuss our first steps in the framework of
lattice QCD towards this enormous task. Dynamical lattice QCD results for the
lowest three Mellin moments of the helicity dependent and independent GPDs are
shown in terms of their corresponding generalized form factors. Implications
for the transverse coordinate space structure of the nucleon as well as the
orbital angular momentum (OAM) contribution of quarks to the nucleon spin are
discussed in some detail.Comment: 5 pages, 5 figures, Talk presented by Ph.H. at Electron-Nucleus
Scattering VIII, Elba, Italy, June 21-25, 2004; typos corrected, minor change
in wording on p.4&
Calculation of Nucleon Electromagnetic Form Factors
The fomalism is developed to express nucleon matrix elements of the
electromagnetic current in terms of form factors consistent with the
translational, rotational, and parity symmetries of a cubic lattice. We
calculate the number of these form factors and show how appropriate linear
combinations approach the continuum limit.Comment: Lattice 2002 (hadronic matrix elements) 3 page
The 2+1 flavor topological susceptibility from the asqtad action at 0.06 fm
We report new data for the topological susceptibility computed on 2+1 flavor
dynamical configurations with lattice spacing 0.06 fm, generated with the
asqtad action. The topological susceptibility is computed by HYP smearing and
compared with rooted staggered chiral perturbation theory as the pion mass goes
to zero. At 0.06 fm, the raw data is already quite close to the continuum
extrapolated values obtained from coarser lattices. These results provide a
further test of the asqtad action with rooted staggered flavors.Comment: 7 pages, 5 figures, talk presented at the XXV International Symposium
on Lattice Field Theory, July 30 - August 4, 2007, Regensburg, German
Transverse Structure of Nucleon Parton Distributions from Lattice QCD
This work presents the first calculation in lattice QCD of three moments of
spin-averaged and spin-polarized generalized parton distributions in the
proton. It is shown that the slope of the associated generalized form factors
decreases significantly as the moment increases, indicating that the transverse
size of the light-cone quark distribution decreases as the momentum fraction of
the struck parton increases.Comment: 4 pages, 1 figur
Calculation of the nucleon axial charge in lattice QCD
Protons and neutrons have a rich structure in terms of their constituents,
the quarks and gluons. Understanding this structure requires solving Quantum
Chromodynamics (QCD). However QCD is extremely complicated, so we must
numerically solve the equations of QCD using a method known as lattice QCD.
Here we describe a typical lattice QCD calculation by examining our recent
computation of the nucleon axial charge.Comment: Prepared for Scientific Discovery through Advanced Computing (SciDAC
2006), Denver, Colorado, June 25-29 200
Lower and upper bounds on the secret key rate for QKD protocols using one--way classical communication
We investigate a general class of quantum key distribution (QKD) protocols
using one-way classical communication. We show that full security can be proven
by considering only collective attacks. We derive computable lower and upper
bounds on the secret key rate of those QKD protocol involving only entropies of
two--qubit density operators. As an illustration of our results, we determine
new bounds for the BB84, the six-state, and the B92 protocol. We show that in
all these cases the first classical processing that the legitimate partners
should apply consists in adding noise. This is precisely why any entanglement
based proof would generally fail here.Comment: minor changes, results for BB84 and B92 adde
The QCD equation of state with asqtad staggered fermions
We report on our result for the equation of state (EOS) with a Symanzik
improved gauge action and the asqtad improved staggered fermion action at
and 6. In our dynamical simulations with 2+1 flavors we use the inexact
R algorithm and here we estimate the finite step-size systematic error on the
EOS. Finally we discuss the non-zero chemical potential extension of the EOS
and give some preliminary results.Comment: 7 pages, 6 figures, presented at Lattice2006(High Temperature and
Density), to appear in Proceedings of Scienc
Nucleon structure in the chiral regime with domain wall fermions on an improved staggered sea
Moments of unpolarized, helicity, and transversity distributions,
electromagnetic form factors, and generalized form factors of the nucleon are
presented from a preliminary analysis of lattice results using pion masses down
to 359 MeV. The twist two matrix elements are calculated using a mixed action
of domain wall valence quarks and asqtad staggered sea quarks and are
renormalized perturbatively. Several observables are extrapolated to the
physical limit using chiral perturbation theory. Results are compared with
experimental moments of quark distributions and electromagnetic form factors
and phenomenologically determined generalized form factors, and the
implications on the transverse structure and spin content of the nucleon are
discussed.Comment: Talks of J.W. Negele and D.B. Renner at Lattice 200
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