238 research outputs found
Dark/Visible Parallel Universes and Big Bang Nucleosynthesis
We develop a model for visible matter-dark matter interaction based on the
exchange of a massive gray boson called herein the Mulato. Our model hinges on
the assumption that all known particles in the visible matter have their
counterparts in the dark matter. We postulate six families of particles five of
which are dark. This leads to the unavoidable postulation of six parallel
worlds, the visible one and five invisible worlds. A close study of big bang
nucleosynthesis (BBN), baryon asymmetries, cosmic microwave background (CMB)
bounds, galaxy dynamics, together with the Standard Model assumptions, help us
to set a limit on the mass and width of the new gauge boson. Modification of
the statistics underlying the kinetic energy distribution of particles during
the BBN is also discussed. The changes in reaction rates during the BBN due to
a departure from the Debye-Hueckel electron screening model is also
investigated.Comment: Invited talk at the Workshops "CompStar: the physics and astrophysics
of compact stars", Tahiti, June 4-8, 2012, "New Directions in Nuclear
Astrophysics", Castiglion Fiorentino, Italy, June 18-22, 2012, and
"Carpathian Summer School of Physics", Sinaia, Romania, June 24 - July 7,
2012. To be published in AIP Proceeding
Malhas móveis para solução numérica de equações diferenciais parciais
Neste trabalho, abordam-se malhas móveis para a resolução numérica de equações diferenciais parciais. Conceitos importantes neste contexto são descritos, bem como indicados trabalhos existentes para a solução de equações diferenciais parciais pelos métodos dos volumes finitos e dos elementos finitos ambos com malhas móveis
A Democratic Gauge Model for Dark/Visible Matter Symmetry
We develop a model for visible matter-dark matter interaction based on the
exchange of a weakly interacting massive gauge boson called herein the WIMG.
Our model hinges on the assumption that all known particles in the visible
matter have their counterparts in the dark matter. We postulate six families of
particles five of which are dark. This leads to the unavoidable postulation of
six parallel worlds, the visible one and five invisible worlds. We give
arguments on particle decays and lifetimes that set a limit on the mass of the
WIMG, the gray boson responsible for the very meager communication among these
worlds. The 5:1 ratio of dark to visible matter is taken for granted
Neinei -- The Neutron Imaging Center at the Brazilian Multipurpose Reactor
Neutron imaging is a non-destructive technique for analyzing a wide class of
materials, such as archaeological or structures of industrial materials.
Technological advances, in recent decades, have had a great impact on the
neutron imaging technique, evolving from simple radiographs using films (2D) to
modern tomography systems with digital processing (3D). The Instituto de
Pesquisas Energ\'eticas e Nucleares (IPEN), in Brazil, houses a 5MW research
nuclear reactor, called IEA-R1, where there is a neutron imaging instrument
located at the beam hole 08 (BH08) with in the
sample position. IEA-R1 is over 60 years old and the future of neutron science
in Brazil, including imaging, will be expanded on a new facility called the
Brazilian Multipurpose Reactor (RMB). The RMB will house a suite of instruments
at the Neutron National Laboratory, including the neutron imaging facility
called Neinei. Inspired by recent work, we have calculated the thermal neutron
flux at the sample position, using the Monte Carlo method, in the Neinei and
compared it to the results obtained with the Neutra (PSI), Antares (FRM II),
BT2 (NIST) and DINGO (OPAL) instruments. The results are promising and provide
avenues for future improvements.Comment: 8 pages, 9 figures. Preprin
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