17 research outputs found
Schwinger-Dyson equations and the quark-antiquark static potential
In lattice QCD, a confining potential for a static quark-antiquark pair can
be computed with the Wilson loop technique. This potential, dominated by a
linear potential at moderate distances, is consistent with the confinement with
a flux tube, an extended and scalar system also directly observable in lattice
QCD. Quantized flux tubes have also been observed in another class of
confinement, the magnetic confinement in type II superconductors. On the other
hand the solution of Schwinger Dyson Equations, say with the Landau gauge
fixing and the truncation of the series of Feynman diagrams, already at the
rainbow level for the self energy and at the ladder level for the Bethe
Salpeter equation, provides a signal of a possible inverse quartic potential in
momentum space derived from one gluon and one ghost exchange, consistent with
confinement. Here we address the successes, difficulties and open problems of
the matching of these two different perspectives of confinement, the
Schwinger-Dyson perspective versus the flux tube perspective.Comment: 12 pages, 18 figures; talk presented at QCD-TNT, Trento, 7-11 sep
200
First study of the gluon-quark-antiquark static potential in SU(3) Lattice QCD
We study the long distance interaction for hybrid hadrons, with a static
gluon, a quark and an antiquark with lattice QCD techniques. A Wilson loop
adequate to the static hybrid three-body system is developed and, using a 24^3
x 48 periodic lattice with beta=6.2 and a ~ 0.075 fm, two different geometries
for the gluon-quark segment and the gluon-antiquark segment are investigated.
When these segments are perpendicular, the static potential is compatible with
confinement realized with a pair of fundamental strings, one linking the gluon
to the quark and another linking the same gluon to the antiquark. When the
segments are parallel and superposed, the total string tension is larger and
agrees with the Casimir Scaling measured by Bali. This can be interpreted with
a type-II superconductor analogy for the confinement in QCD, with repulsion of
the fundamental strings and with the string tension of the first topological
excitation of the string (the adjoint string) larger than the double of the
fundamental string tension.Comment: 4 pages RevTeX, 4 figure
Short-range potentials from QCD at order
We systematically compute the effective short-range potentials arising from
second order QCD-diagrams related to bound states of quarks, antiquarks, and
gluons. Our formalism relies on the assumption that the exchanged gluons are
massless, while the constituent gluons as well as the lightest quarks acquire a
nonvanishing constituent mass because of confinement. The potentials we obtain
include the first relativistic corrections, thus spin-spin terms, spin-orbit
terms, etc. Such effective potentials are expected to be relevant for the
building of accurate potential models describing usual hadrons as well as
exotic ones like glueballs and hybrids. In particular, we compute
for the first time an effective quark-gluon potential, and show the existence
of a quadrupolar interaction term in this case. We also discuss the influence
of a possible nonzero mass for the exchanged gluons.Comment: 33 pages, 4 tables and 12 figures ; typos correcte
Dificuldades enfrentadas pelos indígenas durante a permanência em uma Casa de Saúde Indígena na região Amazônica/Brasil
The structure of the Yang-Mills spectrum for arbitrary simple gauge algebras
The mass spectrum of pure Yang-Mills theory in 3+1 dimensions is discussed
for an arbitrary simple gauge algebra within a quasigluon picture. The general
structure of the low-lying gluelump and two-quasigluon glueball spectrum is
shown to be common to all algebras, while the lightest three-quasigluon
glueballs only exist when the gauge algebra is A, that is in
particular . Higher-lying glueballs are shown to
exist only for the A, D and E gauge
algebras. The shape of the static energy between adjoint sources is also
discussed assuming the Casimir scaling hypothesis and a funnel form; it appears
to be gauge-algebra dependent when at least three sources are considered. As a
main result, the present framework's predictions are shown to be consistent
with available lattice data in the particular case of an
gauge algebra within 't Hooft's large- limit.Comment: 21 pages, 4 figures; remarks added, typos corrected in v2. v3 to
appear in EPJ
Contribuição ao conhecimento dos algas do gênero Euglena (Euglenophyceae) no município do Rio de Janeiro e arredores, Brasil
Lattice QCD static potentials of the meson-meson and tetraquark systems computed with both quenched and full QCD
We revisit the static potential for the system using
SU(3) lattice simulations, studying both the colour singlets groundstate and
first excited state. We consider geometries where the two static quarks and the
two anti-quarks are at the corners of rectangles of different sizes. We analyse
the transition between a tetraquark system and a two meson system with a two by
two correlator matrix. We compare the potentials computed with quenched QCD and
with dynamical quarks. We also compare our simulations with the results of
previous studies and analyze quantitatively fits of our results with anzatse
inspired in the string flip-flop model and in its possible colour excitations.Comment: 24 pages, 17 figures, 14 table