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 $1.0 \times 10^{6}$ $n/cm^{2}s$ 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