18,744 research outputs found
Restoration of U(1) symmetry and meson spectrum in hot or dense matter
We explore the effects of breaking and restoration of chiral and axial
symmetries using an extended three-flavor Nambu-Jona-Lasinio model that
incorporates explicitly the axial anomaly through the 't Hooft interaction. We
implement a temperature (density) dependence of the anomaly coefficient
motivated by lattice results for the topological susceptibility. The spectrum
of scalar and pseudoscalar mesons is analyzed bearing in mind the
identification of chiral partners and the study of its convergence. We also
concentrate on the behavior of the mixing angles that give us relevant
information on the issue under discussion. The results suggest that the axial
part of the symmetry is restored before the possible restoration of the full
U(3)U(3) chiral symmetry might occur.Comment: 9 pages, 5 figures. Talk given at Joint Meeting
Heidelberg-Liege-Paris-Rostock (HLPR 2004), Spa, Belgium, 16-18 Dec 200
Brane bounce-type configurations in a string-like scenario
Brane world six dimensional scenarios with string like metric has been
proposed to alleviate the problem of field localization. However, these models
have been suffering from some drawbacks related with energy conditions as well
as from difficulties to find analytical solutions. In this work, we propose a
model where a brane is made of a scalar field with bounce-type configurations
and embedded in a bulk with a string-like metric. This model produces a sound
AdS scenario where none of the important physical quantities is infinite. Among
these quantities are the components of the energy momentum tensor, which have
its positivity ensured by a suitable choice of the bounce configurations.
Another advantage of this model is that the warp factor can be obtained
analytically from the equations of motion for the scalar field, obtaining as a
result a thick brane configuration, in a six dimensional context. Moreover, the
study of the scalar field localization in these scenario is done.Comment: 15 pages, 5 figures. To appear in Physics Letters
Effects of the restoration of U(1) symmetry on pseudoscalar meson observables
We investigate the restoration of chiral SUSU and axial
U(1) symmetries, at finite temperature and density, in the framework of the
three flavor Nambu-Jona-Lasinio model with anomaly. We implement a temperature
(density) dependence of the anomaly coefficient motivated by lattice results
for the topological susceptibility and we discuss the restoration of symmetries
by analyzing the behavior of the mesonic chiral partners and of the mixing
angles. The results indicate that the axial part of the symmetry is restored
before the possible restoration of the full U(3)U(3) chiral symmetry
can occur.Comment: 4 pages, 1 figure. Contribution to Proc. Int. Europhysics Conf. on
High Energy Physics (HEP2005), 21-27.7.2005, Lisboa, Portuga
Scale insects (Hemiptera: Coccoidea) of ornamental plants from Sao Carlos, Sao Paulo, Brazil
A list of 35 scale insects collected from 72 ornamental plant species in Sao Carlos, Sao Paulo, Brazil is provided. Regarding host specificity, 30 scale insects were polyphagous, 4 oligophagous, and 1 monophagous. A total of 102 coccoid/plant associations are recorded, 29 of which are new host records for the species; 60 are new host records for the species in Brazil. Pulvinaria urbicola Cockerell, 1893 (Coccidae), Phenacoccus similis Granara de Willink, 1983 (Pseudococcidae), and Orthezia molinarii (Morrison, 1952) (Ortheziidae) are recorded for the first time in Brazil. In addition, we describe the injury caused by scale insects on ornamental plants
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