Evolving wormhole geometries within nonlinear electrodynamics

In this work, we explore the possibility of evolving (2+1) and (3+1)-dimensional wormhole spacetimes, conformally related to the respective static geometries, within the context of nonlinear electrodynamics. For the (3+1)-dimensional spacetime, it is found that the Einstein field equation imposes a contracting wormhole solution and the obedience of the weak energy condition. Nevertheless, in the presence of an electric field, the latter presents a singularity at the throat, however, for a pure magnetic field the solution is regular. For the (2+1)-dimensional case, it is also found that the physical fields are singular at the throat. Thus, taking into account the principle of finiteness, which states that a satisfactory theory should avoid physical quantities becoming infinite, one may rule out evolving (3+1)-dimensional wormhole solutions, in the presence of an electric field, and the (2+1)-dimensional case coupled to nonlinear electrodynamics.Comment: 17 pages, 1 figure; to appear in Classical and Quantum Gravity. V2: minor corrections, including a referenc

Phantom energy traversable wormholes

It has been suggested that a possible candidate for the present accelerated expansion of the Universe is ''phantom energy''. The latter possesses an equation of state of the form $\omega\equiv p/\rho<-1$, consequently violating the null energy condition. As this is the fundamental ingredient to sustain traversable wormholes, this cosmic fluid presents us with a natural scenario for the existence of these exotic geometries. Due to the fact of the accelerating Universe, macroscopic wormholes could naturally be grown from the submicroscopic constructions that originally pervaded the quantum foam. One could also imagine an advanced civilization mining the cosmic fluid for phantom energy necessary to construct and sustain a traversable wormhole. In this context, we investigate the physical properties and characteristics of traversable wormholes constructed using the equation of state $p=\omega \rho$, with $\omega<-1$. We analyze specific wormhole geometries, considering asymptotically flat spacetimes and imposing an isotropic pressure. We also construct a thin shell around the interior wormhole solution, by imposing the phantom energy equation of state on the surface stresses. Using the ''volume integral quantifier'' we verify that it is theoretically possible to construct these geometries with vanishing amounts of averaged null energy condition violating phantom energy. Specific wormhole dimensions and the traversal velocity and time are also deduced from the traversability conditions for a particular wormhole geometry. These phantom energy traversable wormholes have far-reaching physical and cosmological implications. For instance, an advanced civilization may use these geometries to induce closed timelike curves, consequently violating causality.Comment: 9 pages, Revtex4. V2: Considerable comments and references added, no physics changes, now 10 pages. Accepted for publication in Physical Review

On thin-shell wormholes evolving in flat FRW spacetimes

We analize the stability of a class of thin-shell wormholes with spherical symmetry evolving in flat FRW spacetimes. The wormholes considered here are supported at the throat by a perfect fluid with equation of state $\mathcal{P}=w\sigma$ and have a physical radius equal to $aR$, where $a$ is a time-dependent function describing the dynamics of the throat and $R$ is the background scale factor. The study of wormhole stability is done by means of the stability analysis of dynamic systems.Comment: 8 pages; to appear in MPL

Melhoramento genético como ferramenta para o crescimento e o desenvolvimento da ovinocultura de corte.

Resumo: Dentre as ações relacionadas à promoção do crescimento e do desenvolvimento de uma atividade pecuária, o melhoramento genético é uma das que mais merece atenção. Para que a ovinocultura de corte no Brasil possa se desenvolver, são necessárias a seleção e a multiplicação de genótipos apropriados aos diversos ecossistemas encontrados no país. Com a finalidade de aperfeiçoar a capacidade de produção dos animais, as ferramentas básicas do melhoramento genético são a seleção e os métodos de acasalamento. Neste trabalho são apresentadas algumas definições fundamentais do melhoramento genético e discutidas formas de sua contribuição para o crescimento da ovinocultura de corte. [Animal breeding as a tool for upgrowth and development of meat sheep sector]. Abstract: Among the actions to promote the growing and the development of an animal breeding activity, the genetic improvement is one of that more attention deserve. Selection and multiplication of genotypes appropriated to several ecossystems found in the country are necessary to the development of meat sheep sector in Brazil. To optimize the production ability of the animals, the basic tools of animal breeding are the selection and the mating methods. In this paper fundamental definitions of animal breeding are presented and forms of its contribution for the upgrowth of meat sheep sector are discussed.Palestra apresentada no XVII Congresso Brasileiro de Reprodução Animal, 31 de maio a 02 de junho de 2007, Curitiba, PR