3,489 research outputs found
Magnetic charge superselection in the deconfined phase of Yang-Mills theory
The vacuum expectation value of an operator carrying magnetic charge is
studied numerically for temperatures above the deconfinement temperature in
SU(2) and SU(3) gauge theory. By analyzing its finite size behaviour, this is
found to be exactly zero in the thermodynamical limit for any T > T_c whenever
the magnetic charge of the operator is different from zero. These results show
that magnetic charge is superselected in the hot phase of quenched QCD.Comment: 4 pages, 6 figures, revtex
Gauge-invariant quark-antiquark nonlocal condensates in lattice QCD
We study, by numerical simulations on a lattice, the behaviour of the
gauge-invariant quark-antiquark nonlocal condensates in the QCD vacuum with
dynamical fermions. A determination is also done in the quenched approximation
and the results are compared with the full-QCD case. The fermionic correlation
length is extracted and compared with the analogous gluonic quantity.Comment: 14 pages, LaTeX file, + 6 PS figure
Renormalization and topological susceptibility on the lattice: SU(2) Yang-Mills theory
The renormalization functions involved in the determination of the
topological susceptibility in the SU(2) lattice gauge theory are extracted by
direct measurements, without relying on perturbation theory. The determination
exploits the phenomenon of critical slowing down to allow the separation of
perturbative and non-perturbative effects. The results are in good agreement
with perturbative computations.Comment: 12 pages + 4 figures (PostScript); report no. IFUP-TH 10/9
Nuevos registros de aves uruguayas
New records from uruguayan birds. Between 1987-1990 I visited 12 times "Termas del RĂo Dayman" (13 km SE from Salto, Uruguay). I recorded 130 species and give information on 10 species
Topological susceptibility in Yang-Mills theory in the vacuum correlator method
We calculate the topological susceptibility of the Yang-Mills vacuum using
the field correlator method. Our estimate for the SU(3) gauge group, \chi^{1/4}
= 196(7) MeV, is in a very good agreement with the results of recent numerical
simulations of the Yang-Mills theory on the lattice.Comment: 5 pages (JETP Letters style
ARTHROPOD PREY AVAILABILITY AND BREEDING OF THE THREATENED STRANGEâTAILED TYRANT (ALECTRURUS RISORA)
ABSTRACT â The Strangeâtailed Tyrant (Alectrurus risora) is an insectivorous flycatcher (Tyrannidae) endemic to the natural tall grasslands of northern Argentina and southern Paraguay. Alectrurus risora has a polygynous mating system and the abundance of arthropods could be a major factor determining the establishment of male breeding territories and the extent of the breeding season, which is shorter than in most other reported tyrant flycatchers. To investigate this hypothesis, we examined the abundance of arthropods in upland and lowland breeding habitats. Upland habitats seem to be preferred for breeding, and usually harbour more nests. Data from one year showed that, for both grasslands, the beginning of the breeding season coincides with a greater availability of arthropods, and that the short reproductive season of A. risora coincides with a general lower availability of prey during February and March in the year we conducted the study. In upland territories, males attracted more females and had more active nests than males holding territories in lowland grasslands. However, the abundance and biomass of total arthropods and of potential prey were higher in lowland than in upland grasslands, with the exception of the abundance of Orthoptera, which was higher in upland habitat and could represent one of the major prey items. Therefore, we conclude that 1) female preference for males in upland grasslands cannot be explained by higher arthropod prey availability, and 2) the availability of arthropod prey may be important in determining the extent of the breeding season, although further, multiannual studies are required to corroborate this hypothesis. RESUMEN â Disponibilidad de artrĂłpodos presa asociados a territorios de reproducciĂłn de un ave en peligro de extinciĂłn, el YetapĂĄ de Collar (Alectrurus risora) El YetapĂĄ de Collar (Alectrurus risora) es un tirĂĄnido insectĂvoro endĂ©mico de los pastizales altos naturales del norte de Argentina y sur de Paraguay, que posee una temporada reproductiva mĂĄs corta que aquella reportada para la mayorĂa de los tirĂĄnidos. Alectrurus risora posee un sistema de apareamiento poligĂnico, y la abundancia de artrĂłpodos podrĂa representar un factor determinante en el establecimiento de los territorios de los machos y en la duraciĂłn de la temporada reproductiva. Con el fin de investigar esta hipĂłtesis examinamos la abundancia de artrĂłpodos en hĂĄbitats reproductivos de pastizales altos y bajos. Los pastizales altos parecen ser mĂĄs utilizados durante la Ă©poca reproductiva y usualmente albergan un mayor nĂșmero de nidos activos. Los datos de un año de muestreo mostraron que el inicio de la temporada reproductiva coincide con el pico de abundancia de artrĂłpodos en ambos pastizales, y que su corta duraciĂłn coincide, para el ĂĄrea en estudio durante el año analizado, con una menor disponibilidad de presas durante los meses de febrero y marzo. En los territorios ubicados en el pastizal alto los machos atrajeron mĂĄs hembras y tuvieron mĂĄs nidos activos que en los territorios de pastizal bajo. Sin embargo, la abundancia y biomasa de artrĂłpodos totales y de presas potenciales fueron mayores en el pastizal bajo, con la excepciĂłn de la abundancia de Orthoptera, que podrĂa representar uno de los tipos principales de presa. A partir de estos resultados, concluimos que 1) la preferencia de las hembras por machos en el pastizal alto no puede ser explicada por una mayor disponibilidad de artrĂłpodos presa, y 2) la disponibilidad de artrĂłpodos presa podrĂa representar un factor importante en la determinaciĂłn de la extensiĂłn de la temporada reproductiva, pero se requieren estudios adicionales, plurianuales, para corroborar esta hipĂłtesis.
Color confinement and dual superconductivity in full QCD
We report on evidence that confinement is related to dual superconductivity
of the vacuum in full QCD, as in quenched QCD. The vacuum is a dual
superconductor in the confining phase, whilst the U(1) magnetic symmetry is
realized a la Wigner in the deconfined phase.Comment: 4 pages, 4 eps figure
Edge Partitions of Optimal -plane and -plane Graphs
A topological graph is a graph drawn in the plane. A topological graph is
-plane, , if each edge is crossed at most times. We study the
problem of partitioning the edges of a -plane graph such that each partite
set forms a graph with a simpler structure. While this problem has been studied
for , we focus on optimal -plane and -plane graphs, which are
-plane and -plane graphs with maximum density. We prove the following
results. (i) It is not possible to partition the edges of a simple optimal
-plane graph into a -plane graph and a forest, while (ii) an edge
partition formed by a -plane graph and two plane forests always exists and
can be computed in linear time. (iii) We describe efficient algorithms to
partition the edges of a simple optimal -plane graph into a -plane graph
and a plane graph with maximum vertex degree , or with maximum vertex
degree if the optimal -plane graph is such that its crossing-free edges
form a graph with no separating triangles. (iv) We exhibit an infinite family
of simple optimal -plane graphs such that in any edge partition composed of
a -plane graph and a plane graph, the plane graph has maximum vertex degree
at least and the -plane graph has maximum vertex degree at least .
(v) We show that every optimal -plane graph whose crossing-free edges form a
biconnected graph can be decomposed, in linear time, into a -plane graph and
two plane forests
New records of <i>Catamblyrhynchus diadema</i> for Northwestern Argentina
The first record of the Plushcap ( <i>Catamblyrhynchus diadema</i>) for Salta province is given based in a collected specimen. New records for Jujuy province are reported. A immature plumage is described and information about the habits is discussed by means ofthe bibliography and field notes
A critical comparison of different definitions of topological charge on the lattice
A detailed comparison is made between the field-theoretic and geometric
definitions of topological charge density on the lattice. Their
renormalizations with respect to continuum are analysed. The definition of the
topological susceptibility, as used in chiral Ward identities, is reviewed.
After performing the subtractions required by it, the different lattice methods
yield results in agreement with each other. The methods based on cooling and on
counting fermionic zero modes are also discussed.Comment: 12 pages (LaTeX file) + 7 (postscript) figures. Revised version.
Submitted to Phys. Rev.
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