Quantum Topology Change in (2 + 1)d

The topology of orientable (2 + 1)d spacetimes can be captured by certain lumps of non-trivial topology called topological geons. They are the topological analogues of conventional solitons. We give a description of topological geons where the degrees of freedom related to topology are separated from the complete theory that contains metric (dynamical) degrees of freedom. The formalism also allows us to investigate processes of quantum topology change. They correspond to creation and annihilation of quantum geons. Selection rules for such processes are derived.Comment: LaTeX file, 33 pages, 10 postscript figures, some typos corrected, references updated, and other minor change

A novel notion of null infinity for c-boundaries and generalized black holes

We give new definitions of null infinity and black hole in terms of causal boundaries, applicable to any strongly causal spacetime $(M,g)$. These are meant to extend the standard ones given in terms of conformal boundaries, and use the new definitions to prove a classic result in black hole theory for this more general context: if the null infinity is regular (i.e. well behaved in a suitable sense) and $(M,g)$ obeys the null convergence condition, then any closed trapped surface in $(M,g)$ has to be inside the black hole region. As an illustration of this general construction, we apply it to the class of generalized plane waves, where the conformal null infinity is not always well-defined. In particular, it is shown that (generalized) black hole regions do not exist in a large family of these spacetimes.Comment: 32 pages, 4 figures. Included new referenc

A Novel Spin-Statistics Theorem in (2 + 1)d Chern-Simons Gravity

It has been known for some time that topological geons in quantum gravity may lead to a complete violation of the canonical spin-statistics relation : there may exist no connection between spin and statistics for a pair of geons. We present an algebraic description of quantum gravity in (2 + 1)d based on the first order formalism of general relativity and show that, although the usual spin-statistics theorem is not valid, statistics is completely determined by spin. Hence, a new spin-statistics theorem can be formulated.Comment: 7 pages, 1 figure,slightly expanded version, but no essential change

Green ear yield in corn growth after cowpea incorporation.

Com irrigação, o milho pode ser cultivado durante praticamente todo o ano, na região Nordeste do Brasil, o que, em muitas áreas, resulta em degradação do solo. O renovado interesse no estudo de rotações culturais com leguminosas tem como objetivo reduzir essa degradação. O objetivo do trabalho foi avaliar os rendimentos de espigas verdes de cultivares de milho(AG 8080, AG 9010 e DKB 333B) após o cultivo da cultivar de caupi Sempre Verde, incorporada ao solo em três épocas. Dois experimentos irrigados (um envolvendo caupi e o outro milho) foram realizados. Os seguintes tratamentos foram aplicados, no delineamento de blocos ao acaso, com dez repetições: sem cultivo de caupi e incorporação do caupi por ocasião do florescimento, ou após quatro colheitas do feijão verde, ou após três colheitas do feijão maduro. As cultivares de milho foram cultivadas em cada uma das áreas do experimento com caupi. Portanto, o experimento com milho seguiu o delineamento de parcelas subdivididas em blocos ao acaso, com dez repetições. A despeito das diferenças entre as quantidades de matéria seca de caupi incorporadas ao solo, não existiram diferenças entre as características químicas do solo, por ocasião do plantio do milho. A não-incorporação do caupi ou sua incorporação, em qualquer época, não teve influência sobre o número e o peso totais de espigas e o número e peso de espigas comercializáveis, empalhadas e despalhadas. A cultivar AG 8080 apresentou os maiores rendimentos

An entirely analytical cosmological model

The purpose of the present study is to show that in a particular cosmological model, with an affine equation of state, one can obtain, besides the background given by the scale factor, Hubble and deceleration parameters, a representation in terms of scalar fields and, more important, explicit mathematical expressions for the density contrast and the power spectrum. Although the model so obtained is not realistic, it reproduces features observed in some previous numerical studies and, therefore, it may be useful in the testing of numerical codes and as a pedagogical tool.Comment: 4 pages (revtex4), 4 figure