Gravitation and Duality Symmetry

By generalizing the Hodge dual operator to the case of soldered bundles, and working in the context of the teleparallel equivalent of general relativity, an analysis of the duality symmetry in gravitation is performed. Although the basic conclusion is that, at least in the general case, gravitation is not dual symmetric, there is a particular theory in which this symmetry shows up. It is a self dual (or anti-self dual) teleparallel gravity in which, due to the fact that it does not contribute to the interaction of fermions with gravitation, the purely tensor part of torsion is assumed to vanish. The ensuing fermionic gravitational interaction is found to be chiral. Since duality is intimately related to renormalizability, this theory may eventually be more amenable to renormalization than teleparallel gravity or general relativity.Comment: 7 pages, no figures. Version 2: minor presentation changes, references added. Accepted for publication in Int. J. Mod. Phys.

Teleparallel origin of the Fierz picture for spin-2 particle

A new approach to the description of spin-2 particle in flat and curved spacetime is developed on the basis of the teleparallel gravity theory. We show that such an approach is in fact a true and natural framework for the Fierz representation proposed recently by Novello and Neves. More specifically, we demonstrate how the teleparallel theory fixes uniquely the structure of the Fierz tensor, discover the transparent origin of the gauge symmetry of the spin 2 model, and derive the linearized Einstein operator from the fundamental identity of the teleparallel gravity. In order to cope with the consistency problem on the curved spacetime, similarly to the usual Riemannian approach, one needs to include the non-minimal (torsion dependent) coupling terms.Comment: 5 pages, Revtex4, no figures. Accepted for publication in Phys. Rev.

Dirac spinor fields in the teleparallel gravity: comment on "Metric-affine approach to teleparallel gravity"

We show that the coupling of a Dirac spinor field with the gravitational field in the teleparallel equivalent of general relativity is consistent. For an arbitrary SO(3,1) connection there are two possibilities for the coupling of the spinor field with the gravitational field. The problems of consistency raised by Y. N. Obukhov and J. G. Pereira in the paper {\it Metric-affine approach to teleparallel gravity} [gr-qc/0212080] take place only in the framework of one particular coupling. By adopting an alternative coupling the consistency problem disappears.Comment: 8 pages, Latex file, no figures, to appear in the Phys. Rev. D as a Commen

Torsion Gravity: a Reappraisal

The role played by torsion in gravitation is critically reviewed. After a description of the problems and controversies involving the physics of torsion, a comprehensive presentation of the teleparallel equivalent of general relativity is made. According to this theory, curvature and torsion are alternative ways of describing the gravitational field, and consequently related to the same degrees of freedom of gravity. However, more general gravity theories, like for example Einstein-Cartan and gauge theories for the Poincare and the affine groups, consider curvature and torsion as representing independent degrees of freedom. By using an active version of the strong equivalence principle, a possible solution to this conceptual question is reviewed. This solution favors ultimately the teleparallel point of view, and consequently the completeness of general relativity. A discussion of the consequences for gravitation is presented.Comment: RevTeX, 34 pages. Review article to be published by Int. J. Mod. Phys.

Trigo EMBRAPA 41: nova cultivar para Minas Gerais, Goiás e Distrito Federal.

A cultivar de trigo (Triticum aestivum L.) EMBRAPA 41 foi criada pela Embrapa - Centro de Pesquisa Agropecuária dos Cerrados (CPAC), em Planaltina, DF. Essa cultivar é o resultado da seleção realizada na descendência do cruzamento entre PF 813 e Polo 1; foi avaliada na fase experimental como linhagem CPAC 88118. A nova cultivar foi recomendada, pela Comissão Centro-Brasileira de Pesquisa de Trigo, para cultivo irrigado durante a estação seca, em 1995, nos estados de Minas Gerais e Goiás e no Distrito Federal. Essa cultivar destaca-se por apresentar estatura média, ciclo precoce, alto potencial de rendimento e por sua superior qualidade industrial. Nas avaliações de resistência a enfermidades, apresentou reação de resistência em relação à ferrugem-do-colmo, causada por Puccinia graminis tritici.Novas Cultivares

Pragas e inimigos naturais presentes nas folhas das plantas de feijão-caupi e milho-verde em cultivo consorciado e com sistema orgânico de produção.

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Produção e qualidade de frutos de cultivares de melancia sob irrigação por gotejamento.

Esta pesquisa foi conduzida no Campo Experimental da Embrapa Meio-Norte, Teresina, PI (05°05? S; 42°48?W e 74,4m), com o objetivo de avaliar a produção e qualidade dos frutos de três cultivares de melancia: o híbrido duplo Top Gun, o híbrido triplo Shadow e a cultivar Crimson Sweet, sob irrigação por gotejamento. Aplicou-se uma lâmina de irrigação diária equivalente a 100% de reposição da ET0. O delineamento experimental foi o de blocos casualizados com quatro repetições e duas amostras por parcela. Foram avaliados os seguintes parâmetros: peso médio dos frutos (kg), número de frutos por planta, produtividade (t.ha-1), fator de forma do fruto (dado pela relação entre a largura e o comprimento do fruto), sólidos solúveis totais (ºBrix), pH, conteúdo de vitamina C (mg/100 g de polpa) e acidez total titulável (% ácido cítrico). A cultivar Crimson Sweet apresentou diferença significativa para peso médio dos frutos (6,13 kg) e fator de forma do fruto (0,92), enquanto a cultivar Top Gun apresentou maior conteúdo de vitamina C (6,71 mg/100 g de polpa) e pH (5,21). A produtividade da variedade Crimson Sweet e Top Gun foi influenciada pelo número de frutos por planta

Teleparallel Versions of Friedmann and Lewis-Papapetrou Spacetimes

This paper is devoted to investigate the teleparallel versions of the Friedmann models as well as the Lewis-Papapetrou solution. We obtain the tetrad and the torsion fields for both the spacetimes. It is shown that the axial-vector vanishes for the Friedmann models. We discuss the different possibilities of the axial-vector depending on the arbitrary functions $\omega$ and $\psi$ in the Lewis-Papapetrou metric. The vector related with spin has also been evaluated.Comment: 13 pages, accepted for publication in GR