420 research outputs found
The quark-photon vertex and meson electromagnetic form factors
The ladder Bethe-Salpeter solution for the dressed photon-quark vertex is
used to study the low-momentum behavior of the pion electromagnetic and the
transition form factors. With model parameters
previously fixed by light meson masses and decay constants, the low-momentum
slope of both form factors is in excellent agreement with the data. In
comparison, the often-used Ball-Chiu Ansatz for the vertex is found to be
deficient; less than half of the obtained is generated by that Ansatz
while the remainder of the charge radius could be attributed to the tail of the
resonance.Comment: 4 pages, 2 figures, uses espcrc1.sty, talk presented at PANIC99,
Uppsala, Swede
Analysis of full-QCD and quenched-QCD lattice propagators
Recent lattice-QCD results for the dressed-gluon propagator are used within
the quark Dyson-Schwinger equation to determine the gluon-quark vertex dressing
necessary to reproduce the lattice-QCD results for the dressed-quark
propagator. Both quenched and full QCD lattice simulations, for a range of low
quark current masses, are analyzed. The chiral extrapolation is made through
this continuum DSE form. Resulting chiral and physical pion observables are
investigated.Comment: Talk given at PANIC 2005 Conference, Santa Fe, October 2005. To be
published in the Proceeding
Quark-gluon vertex dressing and meson masses beyond ladder-rainbow truncation
We include a generalized infinite class of quark-gluon vertex dressing
diagrams in a study of how dynamics beyond the ladder-rainbow truncation
influences the Bethe-Salpeter description of light quark pseudoscalar and
vector mesons. The diagrammatic specification of the vertex is mapped into a
corresponding specification of the Bethe-Salpeter kernel, which preserves
chiral symmetry. This study adopts the algebraic format afforded by the simple
interaction kernel used in previous work on this topic. The new feature of the
present work is that in every diagram summed for the vertex and the
corresponding Bethe-Salpeter kernel, each quark-gluon vertex is required to be
the self-consistent vertex solution. We also adopt from previous work the
effective accounting for the role of the explicitly non-Abelian three gluon
coupling in a global manner through one parameter determined from recent
lattice-QCD data for the vertex. With the more consistent vertex used here, the
error in ladder-rainbow truncation for vector mesons is never more than 10% as
the current quark mass is varied from the u/d region to the b region.Comment: 15 pages, 12 figure
Quark-gluon vertex model and lattice-QCD data
A model for the dressed quark-gluon vertex, at zero gluon momentum, is formed
from a nonperturbative extension of the two Feynman diagrams that contribute at
1-loop in perturbation theory. The required input is an existing ladder-rainbow
model Bethe-Salpeter kernel from an approach based on the Dyson-Schwinger
equations; no new parameters are introduced. The model includes an Ansatz for
the triple-gluon vertex. Two of the three vertex amplitudes from the model
provide a point-wise description of the recent quenched lattice-QCD data. An
estimate of the effects of quenching is made.Comment: 4 pages, 3 figure
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