139 research outputs found
Wave Functions of the Proton Ground State in the Presence of a Uniform Background Magnetic Field in Lattice QCD
We calculate the probability distributions of quarks in the ground state of
the proton, and how they are affected in the presence of a constant background
magnetic field. We focus on wave functions in the Landau and Coulomb gauges. We
observe the formation of a scalar u-d diquark clustering. The overall
distortion of the quark probability distribution under a very large magnetic
field, as demanded by the quantisation conditions on the field, is quite small.
The effect is to elongate the distributions along the external field axis while
localizing the remainder of the distribution.Comment: 15 pages, 18 figure
Quark-gluon vertex in arbitrary kinematics
We compute the quark-gluon vertex in quenched lattice QCD, in the Landau
gauge using an off-shell mean-field O(a)-improved fermion action. The complete
vertex is computed in two specific kinematical limits, while the Dirac-vector
part is computed for arbitrary kinematics. We find a nontrivial and rich tensor
structure, including a substantial infrared enhancement of the interaction
strength regardless of kinematics.Comment: 6 pages, 8 figures, talk by JIS at QCD Down Under, Adelaide, 10-19
March 200
Impact of stout-link smearing in lattice fermion actions
The impact of stout-link smearing in lattice fermion actions is examined
through the consideration of the mass and renormalization functions of the
overlap quark propagator over a variety of smeared configurations. Up to six
sweeps of stout-link smearing are investigated. For heavy quark masses, the
quark propagator is strongly affected by the smearing procedure. For moderate
masses, the effect appears to be negligible. A small effect is seen for light
quark masses, where dynamical mass generation is suppressed through the
smearing procedure.Comment: 7 pages, 3 figures, presented at the XXVII International Symposium on
Lattice Field Theory - LAT2009, July 26-31 2009, Peking University, Beijing,
Chin
Stout-link smearing in lattice fermion actions
The properties of the momentum space quark propagator in Landau gauge are
studied for the overlap quark action in quenched lattice QCD. Numerical
calculations are performed over four ensembles of gauge configurations, where
three are smeared using either 1, 3, or 6 sweeps of stout-link smearing. We
calculate the non-perturbative wave function renormalization function
and the non-perturbative mass function for a variety of bare quark
masses. We find that the wave-function renormalization function is slightly
sensitive to the number of stout-link smearing sweeps. For the mass function we
find the effect of the stout-link smearing algorithm to be small for moderate
to light bare quark masses. For a heavy bare quark mass we find a strong
dependence on the number of smearing sweeps.Comment: 8 pages, 4 figure
A Numerical Approach to Coulomb Gauge QCD
We calculate the ghost two-point function in Coulomb gauge QCD with a simple
model vacuum gluon wavefunction using Monte Carlo integration. This approach
extends the previous analytic studies of the ghost propagator with this ansatz,
where a ladder-rainbow expansion was unavoidable for calculating the path
integral over gluon field configurations. The new approach allows us to study
the possible critical behavior of the coupling constant, as well as the Coulomb
potential derived from the ghost dressing function. We demonstrate that IR
enhancement of the ghost correlator or Coulomb form factor fails to
quantitatively reproduce confinement using Gaussian vacuum wavefunctional
Scaling behavior of quark propagator in full QCD
We study the scaling behavior of the quark propagator on two lattices with
similar physical volume in Landau gauge with 2+1 flavors of dynamical quarks in
order to test whether we are close to the continuum limit for these lattices.
We use configurations generated with an improved staggered (``Asqtad'') action
by the MILC collaboration. The calculations are performed on
lattices with lattice spacing fm and on lattices
with lattice spacing fm. We calculate the quark mass function,
, and the wave-function renormalization function, , for a
variety of bare quark masses. Comparing the behavior of these functions on the
two sets of lattices we find that both and show little
sensitivity to the ultraviolet cutoff.Comment: 6 pages, 5 figure
Unquenched quark propagator in Landau gauge
We present an unquenched calculation of the quark propagator in Landau gauge
with 2+1 flavors of dynamical quarks. We use configurations generated with an
improved staggered (``Asqtad'') action by the MILC collaboration. This quark
action has been seen to have excellent rotational symmetry and scaling
properties in the quenched quark propagator. Quenched and dynamical
calculations are performed on a lattice with a nominal lattice
spacing of fm. The matched quenched and dynamical lattices allow us
to investigate the relatively subtle sea quark effects, and even in the
quenched case the physical volume of these lattices gives access to lower
momenta than our previous study. We calculate the quark mass function and
renormalization function for a variety of valence and sea quark masses.Comment: 7 pages, 6 figure
The FLIC Overlap Quark Propagator
FLIC overlap fermions are a variant of the standard (Wilson) overlap action,
with the FLIC (Fat Link Irrelevant Clover) action as the overlap kernel rather
than the Wilson action. The structure of the FLIC overlap fermion propagator in
momentum space is studied, and a comparison against previous studies of the
Wilson overlap propagator in quenched QCD is performed. To explore the scaling
properties of the propagator for the two actions, numerical calculations are
performed in Landau Gauge across three lattices with different lattice spacing
and similar physical volumes. We find that at light quark masses the acti
ons agree in both the infrared and the ultraviolet, but at heavier masses some
disagreement in the ultraviolet appears. This is attributed to the two action s
having different discretisation errors with the FLIC overlap providing superior
performance in this regime. Both actions scale reasonably, but some scaling
violations are observed
Quark propagator from an improved staggered action in Laplacian and Landau gauges
Studies of gauge dependent quantities are afflicted with Gribov copies, but
Laplacian gauge fixing provides one possible solution to this problem. We
present results for the lattice quark propagator in both Landau and Laplacian
gauges using standard and improved staggered quark actions. The standard
Kogut-Susskind action has errors of \oa{2} while the improved ``Asqtad'' action
has \oa{4}, \oag{2}{2} errors and this improvement is seen in the quark
propagator. We demonstrate the application of tree-level corrections to these
actions and see that Landau and Laplacian gauges produce very similar results.
In addition, we test an ansatz for the quark mass function, with promising
results. In the chiral limit, the infrared quark mass, is found to
be MeV.Comment: 5 pages, 8 figs., Talk given at LHP workshop, Cairn
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