A study of quark-gluon vertices using the lattice Coulomb gauge domain wall fermion (original) (raw)
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Propagator of the lattice Coulomb gauge domain wall fermion
We calculate the propagator of the domain wall fermion (DWF) of the RBC/UKQCD collabora-tion with 2+1 dynamical flavors of 16 3 × 32 × 16 lattice, by applying the conjugate gradient method. We find that the fluctuation of the propagator is small when the momenta are taken along the diagonal of the 4-dimensional lattice. This momentum selection is called cylinder cut. Using propa-gator after cylinder cut, we compare the mass function and the running coupling of the quark-gluon coupling αs,g 1 (q) with those of the Kogut-Susskind (KS) fermion of the MILC collaboration. In the case of DWF, the ambiguity of the phase of the wave function is adjusted such that the overlap of the solution of the conjugate gradient method and the plane wave at the source becomes real. The quark-gluon coupling αs,g 1 (q) of the DWF in the region q > 1.3GeV agrees with ghost-gluon coupling αs(q) that we measured by using the configuration of the MILC collaboration, i.e. enhancement by a factor (1 + c/q 2)...
Physical Review D, 1993
We present a comparison of Coulomb gauge wave functions from 6/g 2 = 6.0 quenched simulations with two simulations which include the effects of dynamical fermions: simulations with two flavors of dynamical staggered quarks and valence Wilson quarks at 6/g 2 = 5.6 and simulations with two flavors of dynamical Wilson quarks and Wilson valence quarks, at 6/g 2 = 5.3. The spectroscopy of these systems is essentially identical. Parameterizations of the wave functions are presented which can be used as interpolating fields for spectroscopy calculations. The sizes of particles are calculated using these parameterized wave functions. The resulting sizes are small, approximately half the sizes of the physical states. The charge radius of the neutron, which provides an indication of the asymmetries between the wave functions of up and down quarks, is calculated. Although the size of the nucleon in these simulations is small, the ratio of the charge radius of the neutron to that of the proton is consistent with the physical value. We find no significant differences between the quenched and dynamical simulations.
Propagator of the Lattice Domain Wall Fermion and the Staggered Fermion
Few-Body Systems, 2009
We calculate the propagator of the domain wall fermion (DWF) of the RBC/UKQCD collaboration with 2+1 dynamical flavors of 16 3 × 32 × 16 lattice in Coulomb gauge, by applying the conjugate gradient method. We find that the fluctuation of the propagator is small when the momenta are taken along the diagonal of the 4-dimensional lattice. Restricting momenta in this momentum region, which is called the cylinder cut, we compare the mass function and the running coupling of the quark-gluon coupling α s,g 1 (q) with those of the staggerd fermion of the MILC collaboration in Landau gauge.
The Landau gauge lattice QCD simulation and the gluon propagator
Nuclear Physics B-proceedings Supplements, 1999
We measured the gluon propagator in the Landau gauge fixed QCD Langevin simulation[2] and studied the infra-red behaviour of the gluon propagator. The (4 3 × 8) lattice siulation was done for quenched β = 3, 4 and 5 and unquenched β = 4, κ = 0.1, 0.15 and 0.2, using each 100 independent samples. The Landau gauge fixing was done by an extension of the Fourier acceleration method with the condition |divA| < 10 −4 , and the field A is related to the link variable by U = expA instead of the usual U-linear definition. We confirmed gauge fixing with smearing preconditioning[3] works perfectly for the purpose of finding the global minimum of the squared norm of the gauge field when β is large (e.g. β = 5). Our simulation results suggests the possibility of a realization of the infra-red behaviour of the Gribov-Zwanziger theory.
Nucleon axial charge from quenched lattice QCD with domain wall fermions and improved gauge action
Nuclear Physics B-proceedings Supplements, 2002
The domain wall fermion (DWF) method, with its almost perfectly preserved chiral symmetry on the lattice, makes the calculation of the nucleon axial charge particularly easy. By maintaining chiral symmetry and using the Ward-Takahashi (WT) identity, one has ZA = ZV and the bare lattice calculation yields the physical value without explicit renormalization. The DBW2 improved gauge action provides further enhancement of the symmetry and hence a more accurate WT identity at coarse lattice spacing. Taking advantage of these methods, we confirmed a significant volume dependence of the nucleon axial charge on (1.2fm) 3 and (2.4fm) 3 lattice volumes.
Lattice gauge theory studies of the gluon propagator
The gluon propagator in Landau gauge is calculated in quenched QCD on a large (32 3 × 64) lattice at β = 6.0. In order to assess finite volume and finite lattice spacing artefacts, we also calculate the propagator on a smaller volume for two different values of the lattice spacing. New structure seen in the infrared region survives conservative cuts to the lattice data, and serves to exclude a number of models that have appeared in the literature.
Lattice quark propagator in fixed gauges
Nuclear Physics B - Proceedings Supplements, 1990
A lattice study of the quenched QCD quark propagator in Landau and Coulomb gauges is reported. We find that m£ itical. the value of the quark propagator pole in the chiral limit, is 290 ± 20 MeV (/? = 5.7) and 350 ± 40 MeV (/? = 6.0). Scaling and gauge dependence of this quantity are discussed.
2007
The effective coupling of QCD is measured by using the gauge configurations produced by the MILC collaboration in which the Kogut Susskind (KS) fermion is incorporated and by using that produced by the RBC/UKQCD collaboration in which the domain wall fermion (DWF) is incorporated. We fix the gauge to the Landau gauge and to the Coulomb gauge. The infrared effective coupling in the Coulomb gauge agrees with the recent extraction at JLab, but that in the Landau gauge shows infrared suppression. The suppression is expected to be due to the color anti-symmetric ghost propagator which in the unquenched configurations has stronger infrared singularity than the color diagonal ghost propagator. The Coulomb form factor in the infrared depends on the kind of the fermion incorporated in the system and the temperature. The quark has the effect of quenching randomness and the fluctuation of the color anti-symmetric ghost propagator is reduced in the unquenched configuration, and the Kugo-Ojima p...
Gauge-variant propagators and the running coupling from lattice QCD
On the occasion of the 70's birthday of Prof. Adriano Di Giacomo we report on recent numerical computations of the Landau gauge gluon and ghost propagators as well as of a non-symmetric MOMscheme ghost-gluon vertex in quenched and full lattice QCD. Special emphasis is paid to the Gribov copy problem and to the unquenching effect. The corresponding running coupling αs(q 2) is found and shown to decrease for q 2 ≤ 0.3 GeV 2 in the infrared limit. No indication for a non-trivial infrared fixed point is seen in agreement with findings from truncated systems of Dyson-Schwinger equations treated on a four-dimensional torus.
Gluon Propagator in the Landau Gauge Fixed Lattice QCD Simulation
Quark Confinement And The Hadron Spectrum III, 2000
We measured the gluon propagator in the Landau gauge fixed QCD Langevin simulation[2] and studied the infra-red behaviour of the gluon propagator. The (4 3 × 8) lattice siulation was done for quenched β = 3, 4 and 5 and unquenched β = 4, κ = 0.1, 0.15 and 0.2, using each 100 independent samples. The Landau gauge fixing was done by an extension of the Fourier acceleration method with the condition |divA| < 10 −4 , and the field A is related to the link variable by U = expA instead of the usual U-linear definition. We confirmed gauge fixing with smearing preconditioning[3] works perfectly for the purpose of finding the global minimum of the squared norm of the gauge field when β is large (e.g. β = 5). Our simulation results suggests the possibility of a realization of the infra-red behaviour of the Gribov-Zwanziger theory.