Accelerated Overlap Fermions

Numerical evaluation of the overlap Dirac operator is difficult since it contains the sign function $\epsilon(H_w)$ of the Hermitian Wilson-Dirac operator $H_w$ with a negative mass term. The problems are due to $H_w$ having very small eigenvalues on the equilibrium background configurations generated in current day Monte Carlo simulations. Since these are a consequence of the lattice discretisation and do not occur in the continuum version of the operator, we investigate in this paper to what extent the numerical evaluation of the overlap can be accelerated by making the Wilson-Dirac operator more continuum-like. Specifically, we study the effect of including the clover term in the Wilson-Dirac operator and smearing the link variables in the irrelevant terms. In doing so, we have obtained a factor of two speedup by moving from the Wilson action to a FLIC (Fat Link Irrelevant Clover) action as the overlap kernel.Comment: 15 pages, 6 figures; V2 contains major revision of the introduction and motivation sections. Conclusion and results unchanged v2.1: formatting chang

FLIC Overlap Fermions

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, $\kappa$, 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.Comment: Lattice2002(chiral

Hybrid Monte Carlo with Fat Link Fermion Actions

The use of APE smearing or other blocking techniques in lattice fermion actions can provide many advantages. There are many variants of these fat link actions in lattice QCD currently, such as FLIC fermions. The FLIC fermion formalism makes use of the APE blocking technique in combination with a projection of the blocked links back into the special unitary group. This reunitarisation is often performed using an iterative maximisation of a gauge invariant measure. This technique is not differentiable with respect to the gauge field and thus prevents the use of standard Hybrid Monte Carlo simulation algorithms. The use of an alternative projection technique circumvents this difficulty and allows the simulation of dynamical fat link fermions with standard HMC and its variants. The necessary equations of motion for FLIC fermions are derived, and some initial simulation results are presented. The technique is more general however, and is straightforwardly applicable to other smearing techniques or fat link actions

Light-Quark FLIC Fermion Simulations of the 1−+1^{-+} Exotic Meson

We investigate the mass of the $1^{-+}$ exotic meson, created with hybrid interpolating fields. Access to light quark masses approaching 25 MeV is facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action, and large ($20^3 \times 40$) lattices. Our results indicate that the $1^{-+}$ exotic exhibits significant curvature close to the chiral limit, and yield a $1^{-+}$ mass in agreement with the $\pi_1 (1600)$ candidate and exclusive of the $\pi_1 (1400)$.Comment: 6 pages, 1 table, 2 figures, talk given at Lattice '05. Removed unccessary figure

The Effect of Fermented Organic Feed Usage On The Health Status of Kampong Chicken

This research aims to determine the effect of the use of fermented organic feed to the health status of Kampong chickens based on the number of bacteria in the intestine and their blood profile. The experiment method with Completely Randomized Design (CRD) was utilized in this study. There were four treatments, T0 = organic feed without fermentation, T1 = organic feed with fermented rice bran, T2 = organic feed with fermented corn and T3 = a combination of fermented rice bran and corn. The fermentation was done using yeast, Saccharomyces cerevisiae, each of these treatments consisted of ten chickens. The parameters measured were the colony number of Escherichia coli, Salmonella sp. in the intestine, the number of erythrocytes, leukocyte, level of hemoglobin and hematocrit, atotal of plasma protein and blood glucose. The data were analyzed by quantitative descriptive analysis. The results show that the fermented rice bran provides the best growth inhibitory effect of E. coli, at 232.6 x 10 cfu/ml, towards Salmonella sp. has been reached by the combination of fermented rice bran and corn, at 794 x 103 cfu/ml. The number of erythrocytes, leukocytes, hematocrit level and a total of plasma protein of blood samples obtained good results by the standard of the literature. The hemoglobin level in rice bran and corn fermented according to the standard level, although in control and the combination of fermented rice bran and corn were less than standard, 6.82 g/dl and 6.30 g/dl respectively.

Centre Vortices in SU(3)

Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.We investigate the effectiveness of using smearing as a means to generate a preconditioning transformation for gauge fields prior to fixing to Maximal Centre Gauge. This still leaves the gaugefixed field in the original gauge orbit. As expected, we find that this preconditioning leads to higher maxima of the gauge-fixing condition, resulting in lower numbers of P-vortices. We also find that removing vortices appears to give a loss of confinement for all cases but that the string tension as measured from vortex-only configurations drops from about 65% to as low as 26% when using the preconditioning method

1−+1^{-+} exotic meson at light quark masses

The mass of the $1^{-+}$ exotic meson, created with hybrid interpolating fields, is explored at light quark masses approaching 25 MeV ($m_\pi / m_\rho \simeq 1/3$). Access to such light quark masses is facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action. Additionally, we make use of large ($20^3 \times 40$) lattices to obtain good control of statistical and finite volume errors. Our results indicate that the $1^{-+}$ exotic exhibits significant curvature close the chiral limit, indicating previous linear extrapolations, far from the chiral regime, have overestimated the mass of the $1^{-+}$. We find for the first time in lattice studies a $1^{-+}$ mass in agreement with the $\pi_1 (1600)$ candidate. We also find a strangeness $\pm$1 $J^P = 1^-$ state with a mass close to 2 GeV.Comment: 8 pages, 11 figures, 3 tables, published versio

Overlap quark propagator near the physical pion mass

The Landau-gauge quark propagator is calculated using overlap valence fermions on 2+1-flavour dynamical clover fermion gauge fields from the PACS-CS collaboration with pion mass mπ∼156 MeVand spatial volume ∼(3fm)³. The observed features of the mass and renormalisation functions are discussed, including a comparison with recent results using O(a)-improved Wilson fermions on 2-flavour dynamical gauge fields.Adam Virgili, Waseem Kamleh, Derek B.Leinwebe

SU(3) centre vortices underpin confinement and dynamical chiral symmetry breaking

The mass function of the nonperturbative quark propagator in SU(3) gauge theory shows only a weak dependence on the vortex content of the gauge configurations. Of particular note is the survival of dynamical mass generation on vortex-free configurations having a vanishing string tension. This admits the possibility that mass generation associated with dynamical chiral symmetry breaking persists without confinement. In this presentation, we examine the low-lying ground-state hadron spectrum of the pi, rho, N and Delta and discover that while dynamical mass generation persists in the vortex-free theory, it is not connected to dynamical chiral symmetry breaking. In this way, centre vortices in SU(3) gauge theory are intimately linked to both confinement and dynamical chiral symmetry breaking. We conclude that centre vortices are the essential underlying feature of the QCD vacuum.Comment: 7 pages, 8 figues. Manuscript accepted for Publication in Phys. Rev.