51,939 research outputs found
Aspects of quark mass generation on a torus
In this talk we report on recent results for the quark propagator on a
compact manifold. The corresponding Dyson-Schwinger equations on a torus are
solved on volumes similar to the ones used in lattice calculations. The
quark-gluon interaction is fixed such that the lattice results are reproduced.
We discuss both the effects in the infinite volume/continuum limit as well as
effects when the volume is small.Comment: 3 pages, 3 figures; talk given by CF at QNP06, Madrid, June 200
Finite volume effects in a quenched lattice-QCD quark propagator
We investigate finite volume effects in the pattern of chiral symmetry
breaking. To this end we employ a formulation of the Schwinger-Dyson equations
on a torus which reproduces results from the corresponding lattice simulations
of staggered quarks and from the overlap action. Studying the volume dependence
of the quark propagator we find quantitative differences with the infinite
volume result at small momenta and small quark masses. We estimate the minimal
box length L below which chiral perturbation theory cannot be applied to be L
\simeq 1.6 fm. In the infinite volume limit we find a chiral condensate of
||_{\bar{MS}}^{2 GeV} = (253 \pm 5.0 MeV)^3, an up/down quark mass of
m_{\bar{MS}}^{2 GeV} = 4.1 \pm 0.3 MeV and a pion decay constant which is only
ten percent smaller than the experimental value.Comment: 19 pages, 8 figures. v2: minor clarifications added, version
published in PR
Form Factors of Baryons in a Confining and Covariant Diquark-Quark Model
We treat baryons as bound states of scalar or axialvector diquarks and a
constituent quark which interact through quark exchange. This description
results as an approximation to the relativistic Faddeev equation for three
quarks which yields an effective Bethe-Salpeter equation. Octet and decuplet
masses and fully four-dimensional wave functions have been computed for two
cases: assuming an essentially pointlike diquark on the one hand, and a diquark
with internal structure on the other hand. Whereas the differences in the mass
spectrum are fairly small, the nucleon electromagnetic form factors are greatly
improved assuming a diquark with structure. First calculations to the
pion-nucleon form factor also suggest improvements.Comment: 11 pages, uses 'aipproc.sty'. Talk given by M.O. at the Workshop
"Effective Theories of Low Energy QCD", Coimbra, Portugal, Sep 10-15 199
Quark Condensates: Flavour Dependence
We determine the q-bar q condensate for quark masses from zero up to that of
the strange quark within a phenomenologically successful modelling of continuum
QCD by solving the quark Schwinger-Dyson equation. The existence of multiple
solutions to this equation is the key to an accurate and reliable extraction of
this condensate using the operator product expansion. We explain why
alternative definitions fail to give the physical condensate.Comment: 9 pages, 7 figures, uses appolb.cls, LaTeX. Talk presented by R.
Williams at the EURIDICE Final Meeting, August 24-27th, 2006, Kazimierz,
Polan
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