21,287 research outputs found
Three-dimensional quantum electrodynamics as an effective interaction
We obtain a Quantum Electrodynamics in 2+1 dimensions by applying a
Kaluza--Klein type method of dimensional reduction to Quantum Electrodynamics
in 3+1 dimensions rendering the model more realistic to application in
solid-state systems, invariant under translations in one direction. We show
that the model obtained leads to an effective action exhibiting an interesting
phase structure and that the generated Chern--Simons term survives only in the
broken phase.Comment: 10 pages in Plain Te
Characterizing the nature of Fossil Groups with XMM
We present an X-ray follow-up, based on XMM plus Chandra, of six Fossil Group
(FG) candidates identified in our previous work using SDSS and RASS data. Four
candidates (out of six) exhibit extended X-ray emission, confirming them as
true FGs. For the other two groups, the RASS emission has its origin as either
an optically dull/X-ray bright AGN, or the blending of distinct X-ray sources.
Using SDSS-DR7 data, we confirm, for all groups, the presence of an r-band
magnitude gap between the seed elliptical and the second-rank galaxy. However,
the gap value depends, up to 0.5mag, on how one estimates the seed galaxy total
flux, which is greatly underestimated when using SDSS (relative to Sersic)
magnitudes. This implies that many FGs may be actually missed when using SDSS
data, a fact that should be carefully taken into account when comparing the
observed number densities of FGs to the expectations from cosmological
simulations. The similarity in the properties of seed--FG and non-fossil
ellipticals, found in our previous study, extends to the sample of X-ray
confirmed FGs, indicating that bright ellipticals in FGs do not represent a
distinct population of galaxies. For one system, we also find that the velocity
distribution of faint galaxies is bimodal, possibly showing that the system
formed through the merging of two groups. This undermines the idea that all
selected FGs form a population of true fossils.Comment: 9 pages, 3 figures. Submitted 01/12/2011 to MNRAS, referee report
received 21/02/2012, accepted 22/02/201
Cosmological constant constraints from observation-derived energy condition bounds and their application to bimetric massive gravity
Among the various possibilities to probe the theory behind the recent
accelerated expansion of the universe, the energy conditions (ECs) are of
particular interest, since it is possible to confront and constrain the many
models, including different theories of gravity, with observational data. In
this context, we use the ECs to probe any alternative theory whose extra term
acts as a cosmological constant. For this purpose, we apply a model-independent
approach to reconstruct the recent expansion of the universe. Using Type Ia
supernova, baryon acoustic oscillations and cosmic-chronometer data, we perform
a Markov Chain Monte Carlo analysis to put constraints on the effective
cosmological constant . By imposing that the cosmological
constant is the only component that possibly violates the ECs, we derive lower
and upper bounds for its value. For instance, we obtain that and within,
respectively, and confidence levels. In addition, about
30\% of the posterior distribution is incompatible with a cosmological
constant, showing that this method can potentially rule it out as a mechanism
for the accelerated expansion. We also study the consequence of these
constraints for two particular formulations of the bimetric massive gravity.
Namely, we consider the Visser's theory and the Hassan and Roses's massive
gravity by choosing a background metric such that both theories mimic General
Relativity with a cosmological constant. Using the
observational bounds along with the upper bounds on the graviton mass we obtain
constraints on the parameter spaces of both theories.Comment: 11 pages, 4 figures, 1 tabl
Resposta funcional de Chrysoperla externa (Hagen) (Neur.: Chrysopidae) alimentada com Rhopalosiphum maidis Fitch (Hom.: Aphididae).
Improved semiclassical density matrix: taming caustics
We present a simple method to deal with caustics in the semiclassical
approximation to the thermal density matrix of a particle moving on the line.
For simplicity, only its diagonal elements are considered. The only ingredient
we require is the knowledge of the extrema of the Euclidean action. The
procedure makes use of complex trajectories, and is applied to the quartic
double-well potential.Comment: 20 pages, 7 figures. Revised version, accepted for publication in
Phys. Rev.
Seleção de primers ISSR para genotipagem de murici.
O muricizeiro, espécie frutífera da família Malpighiaceae, encontra-se disperso em todo o território brasileiro. A Embrapa possui plantas matrizes que precisam ser caracterizadas à nível de DNA. Nesse sentido, os materiais vegetais foram coletados da coleção da Embrapa Amazônia Oriental e conservadas no banco de DNA dessa intuição. As reações de PCR-ISSR foram realizadas testando 100 primer disponíveis em cinco clones de muricizeiro, com objetivo de selecionar os melhores fragmentos polimórficos para os materiais de murici, totalizando no mínimo 100 bandas polimórfica
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