The Brazilian Center for Physics Research is a physics research center in the Urca neighborhood of Rio de Janeiro sponsored by the Brazilian National Council for Scientific and Technological Development , linked to the Ministry of Science and Technology. CBPF was founded in 1949 from a joint effort of Cesar Lattes, José Leite Lopes, and Jayme Tiomno. Throughout its existence, CBPF became an internationally renowned research institution, organizing several international meetings and hosting many renowned physicists, like Richard Feynman and J. Robert Oppenheimer. It was also the starting point of important Brazilian institutions, like the National Institute for Pure and Applied Mathematics , the National Laboratory for Scientific Computation and the National Laboratory of Synchrotron Light . Since its creation, CBPF has been one of the most important Physics research institutions in Brazil, and its graduate program ranks among the best in the country. Wikipedia.
Novello M.,Brazilian Center for Research in Physics (CBPF)
Classical and Quantum Gravity | Year: 2011
The purpose of this work is to show that the gravitational interaction is able to generate mass for all bodies. The condition for this is the existence of an energy distribution represented by the vacuum or the cosmological constant. © 2011 IOP Publishing Ltd.
Liu D.,Ningbo University |
Reboucas M.J.,Brazilian Center for Research in Physics (CBPF)
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
In the standard approach to cosmological modeling in the framework of general relativity, the energy conditions play an important role in the understanding of several properties of the Universe, including singularity theorems, the current accelerating expansion phase, and the possible existence of the so-called phantom fields. Recently, the f(T) gravity has been invoked as an alternative approach for explaining the observed acceleration expansion of the Universe. If gravity is described by a f(T) theory instead of general relativity, there are a number of issues that ought to be reexamined in the framework of f(T) theories. In this work, to proceed further with the current investigation of the limits and potentialities of the f(T) gravity theories, we derive and discuss the bounds imposed by the energy conditions on a general f(T) functional form. The null and strong energy conditions in the framework of f(T) gravity are derived from first principles, namely the purely geometric Raychaudhuri equation along with the requirement that gravity is attractive. The weak and dominant energy conditions are then obtained in a direct approach via an effective energy-momentum tensor for f(T) gravity. Although similar, the energy condition inequalities are different from those of general relativity, but in the limit f(T)=T, the standard forms for the energy conditions in general relativity are recovered. As a concrete application of the derived energy conditions to locally homogeneous and isotropic f(T) cosmology, we use the recent estimated value of the Hubble parameter to set bounds from the weak energy condition on the parameters of two specific families of f(T) gravity theories. © 2012 American Physical Society.
Faci S.,Brazilian Center for Research in Physics (CBPF)
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
We present an SO(2,4)-covariant quantization of the free electromagnetic field in conformally flat spaces (CFSs). A CFS is realized in a six-dimensional space as an intersection of the null cone with a given surface. The smooth move of the latter is equivalent to perform a Weyl rescaling. This allows to transport the SO(2,4)-invariant quantum structure of the Maxwell field from Minkowski space to any CFS. Calculations are simplified and the CFS Wightman two-point functions are given in terms of their Minkowskian counterparts. The difficulty due to gauge freedom is surpassed by introducing two auxiliary fields and using the Gupta-Bleuler quantization scheme. The quantum structure is given by a vacuum state and creators/annihilators acting on some Hilbert space. In practice, only the Hilbert space changes under Weyl rescalings. Also, the quantum SO(2,4)-invariant free Maxwell field does not distinguish between two CFSs. © 2013 American Physical Society.
Deruelle N.,University Paris Diderot |
Rua J.,Brazilian Center for Research in Physics (CBPF)
Journal of Cosmology and Astroparticle Physics | Year: 2014
In this Note we show that Einstein's equations for gravity are generically invariant under "disformations". We also show that the particular subclass when this is not true yields the equations of motion of "Mimetic Gravity". Finally we give the "mimetic" generalization of the Schwarzschild solution. © 2014 IOP Publishing Ltd and Sissa Medialab srl.
Membiela F.A.,Brazilian Center for Research in Physics (CBPF)
Nuclear Physics B | Year: 2014
Although inflation is a natural candidate to generate the lengths of coherence of magnetic fields needed to explain current observations, it needs to break conformal invariance of electromagnetism to obtain significant magnetic amplitudes. Of the simplest realizations are the kinetically-coupled theories f2(φ)Fμν Fμν (or IFF theories). However, these are known to suffer from electric fields backreaction or the strong coupling problem. In this work we shall confirm that such class of theories are problematic to support magnetogenesis during inflationary cosmology. On the contrary, we show that a bouncing cosmology with a contracting phase dominated by an equation of state with p > - ρ/3 can support magnetogenesis, evading the backreaction/strong-coupling problem. Finally, we study safe magnetogenesis in a particular bouncing model with an ekpyrotic-like contracting phase. In this case we found that f2(φ)F2-instabilities might arise during the final kinetic-driven expanding phase for steep ekpyrotic potentials. © 2014 The Author.