154 research outputs found
Dynamically Induced Spontaneous Symmetry Breaking in 3-3-1 Models
We show that in SU(3)_C X SU(3)_L X U(1)_N (3-3-1) models embedded with a
singlet scalar playing the role of the axion, after imposing scale invariance,
dynamical symmetry breaking of Peccei-Quinn symmetry occurs through the
one-loop effective potential for the singlet field. We, then, analyze the
structure of spontaneous symmetry breaking by studying the new scalar potential
for the model, and verify that electroweak symmetry breaking is tightly
connected to the 3-3-1 breaking by the strong constraints among their vacuum
expectation values. This offers a valuable guide to write down the correct
pattern of symmetry breaking for multi-scalar theories. We also obtained that
the accompanying massive pseudo-scalar, instead of acquiring mass of order of
Peccei-Quinn scale as we would expect, develops a mass at a much lower scale, a
consequence solely of the dynamical breaking.Comment: 12 pages, typos corrected, improved text, conclusions unchange
Genetic characterization of cassava (Manihot esculenta) landraces in Brazil assessed with simple sequence repeats
Based on nine microsatellite loci, the aim of this study was to appraise the genetic diversity of 42 cassava (Manihot esculenta) landraces from selected regions in Brazil, and examine how this variety is distributed according to origin in several municipalities in the states of Minas Gerais, São Paulo, Mato Grosso do Sul, Amazonas and Mato Grosso. High diversity values were found among the five above-mentioned regions, with 3.3 alleles per locus on an average, a high percentage of polymorphic loci varying from 88.8% to 100%, an average of 0.265 for observed heterozygosity and 0.570 for gene diversity. Most genetic diversity was concentrated within the regions themselves (HS = 0.52). Cluster analysis and principal component based scatter plotting showed greater similarity among landraces from São Paulo, Mato Grosso do Sul and Amazonas, whereas those from Minas Gerais were clustered into a sub-group within this group. The plants from Mato Grosso, mostly collected in the municipality of General Carneiro, provided the highest differentiation. The migration of human populations is one among the possible reasons for this closer resemblance or greater disparity among plants from the various regions
Optical Light Curves of Supernovae
Photometry is the most easily acquired information about supernovae. The
light curves constructed from regular imaging provide signatures not only for
the energy input, the radiation escape, the local environment and the
progenitor stars, but also for the intervening dust. They are the main tool for
the use of supernovae as distance indicators through the determination of the
luminosity. The light curve of SN 1987A still is the richest and longest
observed example for a core-collapse supernova. Despite the peculiar nature of
this object, as explosion of a blue supergiant, it displayed all the
characteristics of Type II supernovae. The light curves of Type Ib/c supernovae
are more homogeneous, but still display the signatures of explosions in massive
stars, among them early interaction with their circumstellar material. Wrinkles
in the near-uniform appearance of thermonuclear (Type Ia) supernovae have
emerged during the past decade. Subtle differences have been observed
especially at near-infrared wavelengths. Interestingly, the light curve shapes
appear to correlate with a variety of other characteristics of these
supernovae. The construction of bolometric light curves provides the most
direct link to theoretical predictions and can yield sorely needed constraints
for the models. First steps in this direction have been already made.Comment: To be published in:"Supernovae and Gamma Ray Bursters", Lecture Notes
in Physics (http://link.springer.de/series/lnpp
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