27 research outputs found
Scaling behavior of the overlap quark propagator in Landau gauge
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 toward
the continuum limit. We have calculated the nonperturbative momentum-dependent
wave function renormalization function Z(p) and the nonperturbative mass
function M(p) for a variety of bare quark masses and perform an extrapolation
to the chiral limit. We find the behavior of Z(p) and M(p) are in reasonable
agreement between the two finer lattices in the chiral limit, however the data
suggest that an even finer lattice is desirable. The large momentum behavior is
examined to determine the quark condensate.Comment: 9 pages, 5 figures, Revtex 4. Streamlined presentation, additional
data. Final versio
Improved Landau Gauge Fixing and Discretisation Errors
Lattice discretisation errors in the Landau gauge condition are examined. An
improved gauge fixing algorithm in which order a^2 errors are removed is
presented. Order a^2 improvement of the gauge fixing condition displays the
secondary benefit of reducing the size of higher-order errors. These results
emphasise the importance of implementing an improved gauge fixing condition.Comment: LATTICE99 (Improvement and Renormalization), 3 pages, 1 figur
Cooling for instantons and the Wrath of Nahm
The dynamics of instantons and anti-instantons in lattice QCD can be studied
by analysing the action and topological charge of configurations as they
approach a self-dual or anti-self-dual state, i.e. a state in which S/S_0=|Q|.
We use cooling to reveal the semi-classical structure of the configurations we
study. Improved actions which eliminate discretization errors up to and
including O(a^4) are used to stabilise instantons as we cool for several
thousand sweeps. An analogously improved lattice version of the continuum
field-strength tensor is used to construct a topological charge free from
O(a^4) discretization errors. Values of the action and topological charge
obtained with these improved operators approach mutually-consistent integer
values to within a few parts in 10^4 after several hundred cooling sweeps.
Analysis of configurations with |Q| \approx 1 and |Q| \approx 2 supports the
hypothesis that a self-dual |Q|=1 configuration cannot exist on the 4-torus.Comment: 5 pages, 4 figures, talk presented at the workshop on Lattice Hadron
Physics, Cairns Australia, July 200
Towards the Continuum Limit of the Overlap Quark Propagator in Landau Gauge
The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations were done on two lattices with different lattice spacing and
similar physical volumes to explore the quark propagator in the continuum
limit. We have calculated the nonperturbative wavefunction renormalization
function and the nonperturbative mass function for a variety of
bare quark masses and perform a simple linear extrapolation to the chiral
limit. We find the behaviour of and in the chiral limit are in
good agreement between the two lattices.Comment: 3 pages, 2 figures, talk, Lattice2002(Chiral Fermion
Gluon Propagator on Coarse Lattices in Laplacian Gauges
The Laplacian gauge is a nonperturbative gauge fixing that reduces to Landau
gauge in the asymptotic limit. Like Landau gauge, it respects Lorentz
invariance, but it is free of Gribov copies; the gauge fixing is unambiguous.
In this paper we study the infrared behavior of the lattice gluon propagator in
Laplacian gauge by using a variety of lattices with spacings from
to 0.35 fm, to explore finite volume and discretization effects. Three
different implementations of the Laplacian gauge are defined and compared. The
Laplacian gauge propagator has already been claimed to be insensitive to finite
volume effects and this is tested on lattices with large volumes.Comment: RevTex 4.0, 14 pages, 9 colour figures; Correction to Reference
Infrared Behavior of the Gluon Propagator on a Large Volume Lattice
The first calculation of the gluon propagator using an order a^2 improved
action with the corresponding order a^2 improved Landau gauge fixing condition
is presented. The gluon propagator obtained from the improved action and
improved Landau gauge condition is compared with earlier unimproved results on
similar physical lattice volumes of 3.2^3 \times 6.4 fm^4. We find agreement
between the improved propagator calculated on a coarse lattice with lattice
spacing a = 0.35 fm and the unimproved propagator calculated on a fine lattice
with spacing a = 0.10 fm. This motivates us to calculate the gluon propagator
on a coarse large-volume lattice 5.6^3 \times 11.2 fm^4. The infrared behavior
of previous studies is confirmed in this work. The gluon propagator is enhanced
at intermediate momenta and suppressed at infrared momenta. Therefore the
observed infrared suppression of the Landau gauge gluon propagator is not a
finite volume effect.Comment: 8 pages, 4 figures, minor typos corrected and repsonse to referees
comment
Novel fat-link fermion actions
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link
clover fermion action in which only the irrelevant operators of the fermion
action are constructed using smeared links. The simulations are performed on a
16^3 X 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with
n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat Link
Irrelevant Clover (FLIC) action provides scaling which is superior to
mean-field improvement, and offers advantages over nonperturbative O(a)
improvement.Comment: 5 pages, 2 figures, talk given by J.Zanotti at LHP 2001 workshop,
Cairns, Australi
Baryon resonances from a novel fat-link fermion action
We present first results for masses of positive and negative parity excited
baryons in lattice QCD using an O(a^2) improved gluon action and a Fat Link
Irrelevant Clover (FLIC) fermion action in which only the irrelevant operators
are constructed with fat links. The results are in agreement with earlier
calculations of N^* resonances using improved actions and exhibit a clear mass
splitting between the nucleon and its chiral partner, even for the Wilson
fermion action. The results also indicate a splitting between the lowest J^P =
1/2^- states for the two standard nucleon interpolating fields.Comment: 5 pages, 3 figures, talk given by W.Melnitchouk at LHP 2001 workshop,
Cairns, Australi
Multiplicative renormalizability and quark propagator
The renormalized Dyson-Schwinger equation for the quark propagator is
studied, in Landau gauge, in a novel truncation which preserves multiplicative
renormalizability. The renormalization constants are formally eliminated from
the integral equations, and the running coupling explicitly enters the kernels
of the new equations. To construct a truncation which preserves multiplicative
renormalizability, and reproduces the correct leading order perturbative
behavior, non-trivial cancellations involving the full quark-gluon vertex are
assumed in the quark self-energy loop. A model for the running coupling is
introduced, with infrared fixed point in agreement with previous
Dyson-Schwinger studies of the gauge sector, and with correct logarithmic tail.
Dynamical chiral symmetry breaking is investigated, and the generated quark
mass is of the order of the extension of the infrared plateau of the coupling,
and about three times larger than in the Abelian approximation, which violates
multiplicative renormalizability. The generated scale is of the right size for
hadronic phenomenology, without requiring an infrared enhancement of the
running coupling.Comment: 17 pages; minor corrections, comparison to lattice results added;
accepted for publication in Phys. Rev.
On practical problems to compute the ghost propagator in SU(2) lattice gauge theory
In SU(2) lattice pure gauge theory we study numerically the dependence of the
ghost propagator G(p) on the choice of Gribov copies in Lorentz (or Landau)
gauge. We find that the effect of Gribov copies is essential in the scaling
window region, however, it tends to decrease with increasing beta. On the other
hand, we find that at larger beta-values very strong fluctuations appear which
can make problematic the calculation of the ghost propagator.Comment: 15 pages, 5 postscript figures. 2 Figures added Revised version as to
be published in Phys.Rev.