[en] The action of the overlap-Dirac operator on a vector is typically implemented indirectly through a multi-shift conjugate gradient solver. The compute-time required depends upon the condition number, κ, of the matrix that is used as the overlap kernel. While the Wilson action is typically used as the overlap kernel, the FLIC (Fat Link Irrelevant Clover) action has an improved condition number and provides up to a factor of two speedup in evaluating the overlap action. We summarize recent progress on the use of FLIC overlap fermions

[en] We compute non-perturbatively the renormalisation constants of composite operators on a 16³ x 32 lattice with lattice spacing a = 0.093 fm for the overlap fermion action by using the regularisation independent (RI) scheme. The quenched gauge configurations are generated by tadpole improved plaquette plus rectangle action. We test the perturbative continuum relation Z_A = Z_V and Z_S = Z_P and find that they agree well above μ = 1.6 GeV. We also perform a Renormalisation Group analysis at the next-to-next-to-leading order and convert the renormalisation constants to the MSbar scheme

[en] The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a) improvement and allows efficient access to the light quark-mass regime. FLIC fermions enable the construction of the nonperturbatively O(a)-improved conserved vector current without the difficulties associated with the fine tuning of the improvement coefficients. The simulations are performed with an O(a²) mean-field improved plaquette-plus-rectangle gluon action on a 20³ x 40 lattice with a lattice spacing of 0.128 fm, enabling the first simulation of baryon form factors at light quark masses on a large volume lattice. Magnetic moments, electric charge radii and magnetic radii are extracted from these form factors, and show interesting chiral nonanalytic behavior in the light quark mass regime

[en] We present results on hadron masses and quark condensate from Neuberger's overlap fermion. The scaling and chiral properties and finite volume effects from this new Dirac operator are studied. We find that the generalized Gell-Mann-Oakes-Renner relation is well satisfied down to the physical u and d quark mass range. We find that in the range of the lattice spacing we consider, the π and σ masses at a fixed m/_π./m_σ ratio have weak O(a²) dependence

[en] We report our calculation of the pion decay constant f_π, the axial renormalization constant Z_A, and the quenched chiral logarithms from the overlap fermions. The calculation is done on a quenched 20⁴ lattice at a 0.148 fm using tree level tadpole improved gauge action. The smallest pion mass we reach is about 280 MeV. The lattice size is about 4 times the Compton wavelength of the lowest mass pion

[en] 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(p²) and the nonperturbative mass function M(p²) for a variety of bare quark masses and extrapolate to the chiral limit. We find the behavior of Z(i²) and M(P²) are in good agreement for the two finer lattices in the chiral limit. The quark condensate is also calculated

[en] We report results on hadron masses, fitting of the quenched chiral log, and quark masses from Neuberger's overlap fermion on a quenched 20⁴ lattice with lattice spacing a = 0.15 fm. We used the improved gauge action which is shown to lower the density of small eigenvalues for H² as compared to the Wilson gauge action. This makes the calculation feasible on 64 nodes of CRAY-T3E. Also presented is the pion mass on a small volume (6³ x 12 with a Wilson gauge action at β = 5.7). We find that for configurations that the topological charge Q ≠ 0, the pion mass tends to a constant and for configurations with trivial topology, it approaches zero possibly linearly with the quark mass

[en] Using mean--field improved gauge field configurations, we compare the results obtained for the quark propagator from Wilson fermions and Overlap fermions on a 12³ x 24 lattice at a spacing of a = 0.125(2) fm

[en] The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a) improvement and allows efficient access to the light quark-mass regime. FLIC fermions enable the construction of the nonperturbatively O(a)-improved conserved vector current without the difficulties associated with the fine tuning of the improvement coefficients. The simulations are performed with an O(a²) mean-field improved plaquette-plus-rectangle gluon action on a 20³ x 40 lattice with a lattice spacing of 0.128 fm, enabling the first simulation of baryon form factors at light quark masses on a large volume lattice. Magnetic moments, electric charge radii and magnetic radii are extracted from these form factors, and show interesting chiral nonanalytic behavior in the light quark mass regime

[en] 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 a and similar physical volumes to explore the quark propagator in the continuum limit. We have calculated the nonperturbative wavefunction renormalization function Z(p) and the nonperturbative mass function M(p) for a variety of bare quark masses and perform a simple linear extrapolation to the chiral limit. We find the behaviour of Z(p) and M(p) in the chiral limit are in good agreement between the two lattices