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 $28^3\times 96$ lattices with lattice spacing $a = 0.09$ fm and on $20^3\times 64$ lattices with lattice spacing $a = 0.12$ fm. We calculate the quark mass function, $M(q^2)$, and the wave-function renormalization function, $Z(q^2)$, for a variety of bare quark masses. Comparing the behavior of these functions on the two sets of lattices we find that both $Z(q^2)$ and $M(q^2)$ 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 $Z(p^2)$ and the nonperturbative mass function $M(p^2)$ for a variety of bare quark masses and extrapolate to the chiral limit. We find the behavior of $Z(p^2)$ and $M(p^2)$ 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 $^{236}$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 $\Omega \pi$ = 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 ${\cal O}(a)$ errors. We present results using the standard Wilson fermion kernel in the overlap formalism on a $12^3\times 24$ lattice at a spacing of 0.125 fm. We obtain the nonperturbative momentum-dependent wavefunction renormalization function $Z(p)$ and the nonperturbative mass function $M(p)$ 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