470 research outputs found
The spin structure of the Lambda hyperon in quenched lattice QCD
It has been suggested to use the production of Lambda hyperons for
investigating the nucleon spin structure. The viability of this idea depends
crucially on the spin structure of the Lambda. Using nonperturbatively O(a)
improved Wilson fermions in the quenched approximation we have studied matrix
elements of two-quark operators in the Lambda. We present results for the axial
vector current, which give us the contributions of the u, d, and s quarks to
the Lambda spin.Comment: Lattice2001(matrixelement), 3 pages, 2 figure
Low-lying fermion modes of Nf=2 improved Wilson fermions
We present preliminary results for the topological charge and susceptibility
determined from the low-lying eigenmodes of the Wilson-Dirac operator. These
modes have been computed on dynamical configurations with Nf=2
non-perturbatively improved Wilson fermions. We compare our results with the
eigenmodes of fermions in the quenched approximation.Comment: Lattice2001(confinement), 3 pages, 5 Figure
A lattice determination of moments of unpolarised nucleon structure functions using improved Wilson fermions
Within the framework of quenched lattice QCD and using O(a) improved Wilson
fermions and non-perturbative renormalisation, a high statistics computation of
low moments of the unpolarised nucleon structure functions is given. Particular
attention is paid to the chiral and continuum extrapolations.Comment: LaTeX, 66 pages, 22 figure
The electric dipole moment of the nucleon from simulations at imaginary vacuum angle theta
We compute the electric dipole moment of proton and neutron from lattice QCD
simulations with N_f=2 flavors of dynamical quarks at imaginary vacuum angle
theta. The calculation proceeds via the CP odd form factor F_3. A novel feature
of our calculation is that we use partially twisted boundary conditions to
extract F_3 at zero momentum transfer. As a byproduct, we test the QCD vacuum
at nonvanishing theta.Comment: 22 pages, 10 figure
Excited nucleon spectrum using a non-perturbatively improved clover fermion action
We discuss the extraction of negative-parity baryon masses from lattice QCD
calculations. The mass of the lowest-lying negative-parity state
is computed in quenched lattice QCD using an -improved clover
fermion action, and a splitting found with the nucleon mass. The calculation is
performed on two lattice volumes, and three lattice spacings enabling a study
of both finite-volume and finite-lattice-spacing uncertainties. A measurement
of the first excited radial excitation of the nucleon finds a mass considerably
larger than that of the negative-parity ground state, in accord with other
lattice determinations but in disagreement with experiment. Results are also
presented for the lightest negative-parity state.Comment: 7 pages, 5 figures, uses espcrc2. Talk presented at Workshop on
Lattice Hadron Physics, Colonial Club Resort, Cairns, Australia, July 9-18,
2001. Corrected error in determination of mass of excited, positive-parity
nucleon resonanc
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