7,311 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
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The lattice gluon propagator in renormalizable gauges
We study the SU(3) gluon propagator in renormalizable gauges
implemented on a symmetric lattice with a total volume of (3.25 fm) for
values of the guage fixing parameter up to . As expected, the
longitudinal gluon dressing function stays constant at its tree-level value
. Similar to the Landau gauge, the transverse gauge gluon
propagator saturates at a non-vanishing value in the deep infrared for all
values of studied. We compare with very recent continuum studies and
perform a simple analysis of the found saturation with a dynamically generated
effective gluon mass.Comment: 6 pages, 4 figure
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
Gluons at finite temperature
The gluon propagator is investigated at finite temperature via lattice simulations. In particular, we discuss its interpretation as a massive-type bosonic propagator. Moreover, we compute the corresponding spectral density and study the violation of spectral positivity. Finally, we explore the dependence of the gluon propagator on the phase of the Polyakov loop
Adubos orgânico e mineral fosfatado de solubilidade gradual afetando atributos quÃmicos do solo e caracterÃsticas agronômicas em berinjela.
O objetivo deste trabalho foi estudar o efeito de doses crescentes de esterco bovino (EB) e de termofosfato magnesiano (TM) sobre os atributos quÃmicos de um solo, submetido ao preparo e adubação complementar aplicadas ao cultivo da berinjela, e as correlações canônicas entre as caracterÃsticas agronômicas da planta com as caracterÃsticas quÃmicas do solo
The relationship between ENSO and Paraná River flow
International audienceSeveral studies indicate that there is a relationship between the climatic variability in the South American continent and alterations of the position and intensity of the heat sources in the equatorial region. The El Niño phenomenon can influence the precipitation over some regions of South America such as the Brazilian Northeast, Amazonia, South of Brazil and Uruguay. Over 80% of Brazil's energy comes from hydropower, and decisions concerning future availability and pricing require forecasts of river flow, ideally several months in advance. In this work the relationship between the Paraná River flow and the ENSO (El Niño/Southern Oscillation) mode is investigated and statistical forecasts of river flow are tested. An evaluation of the relationship between the Pacific sea surface temperature and the Paraná River flow indicates an ENSO pattern over the equatorial Pacific. The time series of the ENSO mode obtained by applying principal components analysis on the sea surface temperature (SST) were used as predictors for the Paraná River flow forecast. Improvement in the model forecast skill is also obtained by considering the lagged river flow time series as a predictor
O uso de parâmetros de solo como indicadores em programas de pagamentos por serviços ambientais
Os Projetos de Pagamento por Serviços Ambientais atuam principalmente na conservação de áreas remanescentes das florestas, regeneração assistida em bacias hidrográficas e restauração florestal. Produtores são recompensados por preservarem e restaurarem ecossistemas naturais, adotando um manejo sustentável, principalmente em florestas localizadas em áreas de nascentes, em matas ciliares e em áreas de captação. O monitoramento e a avaliação do progresso de programas de PSA são baseados em indicadores, que servem para identificar a atual situação e qualidade do que foi planejado, além de fornecer subsÃdios para a correção de possÃveis problemas detectados. Definir precisamente o que será monitorado, quais os indicadores que serão utilizados e como comprovar o benefÃcio das atividades é um dos maiores desafios dos sistemas de PSA
Teleportation of entangled states without Bell-state measurement
In a recent paper [Phys. Rev. A 70, 025803 (2004)] we presented a scheme to
teleport an entanglement of zero- and one-photon states from a bimodal cavity
to another one, with 100% success probability. Here, inspired on recent results
in the literature, we have modified our previous proposal to teleport the same
entangled state without using Bell-state measurements. For comparison, the time
spent, the fidelity, and the success probability for this teleportation are
considered.Comment: 4 pages, 1 figure, published in Phys. Rev. A 72, 045802 (2005
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