3,536 research outputs found
Lattice quark propagator with staggered quarks in Landau and Laplacian gauges
We report on the lattice quark propagator using standard and improved
Staggered quark actions, with the standard, Wilson gauge action. The standard
Kogut-Susskind action has errors of \oa{2} while the ``Asqtad'' action has
\oa{4}, \oag{2}{2} errors. The quark propagator is interesting for studying the
phenomenon of dynamical chiral symmetry breaking and as a test-bed for
improvement. Gauge dependent quantities from lattice simulations may be
affected by Gribov copies. We explore this by studying the quark propagator in
both Landau and Laplacian gauges. Landau and Laplacian gauges are found to
produce very similar results for the quark propagator.Comment: 11 pages, 15 figure
Modelling the quark propagator
The quark propagator is at the core of lattice hadron spectrum calculations
as well as studies in other nonperturbative schemes. We investigate the quark
propagator with an improved staggered action (Asqtad) and an improved gluon
action, which provides good quality data down to small quark masses. This is
used to construct ans\"{a}tze suitable for model hadron calculations as well as
adding to our intuitive understanding of QCD.Comment: Lattice2002(spectrum
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
Scaling Behavior of the Landau Gauge Overlap Quark Propagator
The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations are done on three lattices with different lattice spacings and
similar physical volumes to explore the approach of the quark propagator
towards the continuum limit. We have calculated the nonperturbative
momentum-dependent wavefunction renormalization function and the
nonperturbative mass function for a variety of bare quark masses and
extrapolate to the chiral limit.
We find the behavior of and are in good agreement for the
two finer lattices in the chiral limit. The quark condensate is also
calculated.Comment: 3 pages, Lattice2003(Chiral fermions
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
Emission of Scission Neutrons in the Sudden Approximation
At a certain finite neck radius during the descent of a fissioning nucleus
from the saddle to the scission point, the attractive nuclear forces can no
more withstand the repulsive Coulomb forces producing the neck rupture and the
sudden absorption of the neck stubs by the fragments. At that moment, the
neutrons, although still characterized by their pre-scission wave functions,
find themselves in the newly created potential of their interaction with the
separated fragments. Their wave functions become wave packets with components
in the continuum. The probability to populate such states gives evidently the
emission probability of neutrons at scission. In this way, we have studied
scission neutrons for the fissioning nucleus U, using two-dimensional
realistic nuclear shapes. Both the emission probability and the distribution of
the emission points relative to the fission fragments strongly depend on the
quantum numbers of the pre-scission state from which the neutron is emitted. In
particular it was found that states with = 1/2+ dominate the
emission. Depending on the assumed pre- and post-scission configurations and on
the emission-barrier height, 30 to 50% of the total scission neutrons are
emitted from 1/2+ states. Their emission points are concentrated in the region
between the newly separated fragments. The upper limit for the total number of
neutrons per scission event is predicted to lie between 0.16 and 1.73
(depending on the computational assumptions).Comment: 31 pages, 16 figures, 2 table
Preconditioning Maximal Center Gauge with Stout Link Smearing in SU(3)
Center vortices are studied in SU(3) gauge theory using Maximal Center Gauge
(MCG) fixing. Stout link smearing and over-improved stout link smearing are
used to construct a preconditioning gauge field transformation, applied to the
original gauge field before fixing to MCG. We find that preconditioning
successfully achieves higher gauge fixing maxima. We observe a reduction in the
number of identified vortices when preconditioning is used, and also a
reduction in the vortex-only string tension.Comment: 9 pages, 4 figure
Overlap Quark Propagator in Landau Gauge
The properties of the quark propagator in Landau gauge in quenched QCD are examined for the overlap quark action. The overlap quark action satisfies the Ginsparg-Wilson relation and as such provides an exact lattice realization of chiral symmetry. This in turn implies that the quark action is free of errors. We present results using the standard Wilson fermion kernel in the overlap formalism on a lattice at a spacing of 0.125 fm. We obtain the nonperturbative momentum-dependent wavefunction renormalization function and the nonperturbative mass function for a variety of bare masses. We perform a simple extrapolation to the chiral limit for these functions. We clearly observe the dynamically generated infrared mass and confirm the qualitative behavior found for the Landau gauge quark propagator in earlier studies. We attempt to extract the quark condensate from the asymptotic behavior of the mass function in the chiral limit
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