Coupled quintessence and vacuum decay

We discuss observational consequences of a class of cosmological models characterized by the dilution of pressureless matter attenuated with respect to the usual $a^{-3}$ scaling due to the decay of vacuum energy. We carry out a joint statistical analysis of observational data from the new \emph{gold} sample of 182 SNe Ia, recent estimates of the CMB shift parameter, and BAO measurements from the SDSS to show that such models favor the decay of vacuum only into the dark matter sector, and that the separately conserved baryons cannot be neglected. In order to explore ways to more fundamentally motivated models, we also derive a coupled scalar field version for this general class of vacuum decay scenarios.Comment: 6 pages, 3 figures, LaTe

Future dynamics in f(R) theories

The $f(R)$ gravity theories provide an alternative way to explain the current cosmic acceleration without invoking dark energy matter component. However, the freedom in the choice of the functional forms of $f(R)$ gives rise to the problem of how to constrain and break the degeneracy among these gravity theories on theoretical and/or observational grounds. In this paper to proceed further with the investigation on the potentialities, difficulties and limitations of $f(R)$ gravity, we examine the question as to whether the future dynamics can be used to break the degeneracy between $f(R)$ gravity theories by investigating the future dynamics of spatially homogeneous and isotropic dust flat models in two $f(R)$ gravity theories, namely the well known $f(R) = R + \alpha R^{n}$ gravity and another by A. Aviles et al., whose motivation comes from the cosmographic approach to $f(R)$ gravity. To this end we perform a detailed numerical study of the future dynamic of these flat model in these theories taking into account the recent constraints on the cosmological parameters made by the Planck team. We show that besides being powerful for discriminating between $f(R)$ gravity theories, the future dynamics technique can also be used to determine the fate of the Universe in the framework of these $f(R)$ gravity theories. Moreover, there emerges from our numerical analysis that if we do not invoke a dark energy component with equation-of-state parameter $\omega < -1$ one still has dust flat FLRW solution with a big rip, if gravity deviates from general relativity via $f(R) = R + \alpha R^n$. We also show that FLRW dust solutions with $f''<0$ do not necessarily lead to singularity.Comment: 12 pages, 8 figures. V2: Generality and implications of the results are emphasized, connection with the recent literature improved, typos corrected, references adde

Scalar field description of decaying-Λ\Lambda cosmologies

The conditions under which cosmologies driven by time varying cosmological terms can be described by a scalar field coupled to a perfect fluid are discussed. An algorithm to reconstruct potentials dynamically and thermodynamically analogue to given phenomenological $\Lambda$ models is presented. As a worked example, the deflationary cosmology, which evolves from a pure de Sitter vacuum state to a slightly modified FRW cosmology is considered. It is found that this is an example of nonsingular warm inflation with an asymptotic exponential potential. Differences with respect to other scalar field descriptions of decaying vacuum cosmologies are addressed and possible extensions are indicated.Comment: 12 pages, revtex, references added, corrected typos and minor text change

Capacidade predatória e aspectos biológicos de Chrysoperla externa (Hagen , 1861) (Neuroptera: Chrysopidae) alimentada com Rhopalosiphum, maidis (Fitch, 1856) (Hemiptera: Aphididae).

Objetivou-se estudar alguns aspectos biológicos. a capacidade predatória. e a resposta funcional de larvas de Chrysoperla externa (Hagen) alimentadas com ninfas de segundo e terceiro ínstares do pulgão Rhopalosiphum maidis (Fitch). em cinco densidades. Os ensaios foram conduzidos em câmaras climatizadas reguladas a 25 +/- 1°C. UR de 70 +/- 10% e fotofase de 12 horas. Para o estudo de biologia e capacidade predatória. o delineamento foi inteiramente casualizado. com cinco repetições e oito indivíduos/repetição. totalizando 40 larvas e. para a resposta funcional. os tratamentos corresponderam a cinco densidades de presa e cinco repetições com dois indivíduos/repetição. As observações foram realizadas às 24. 48 horas e no final de cada instar. O consumo aumentou proporcionalmente em função do estádio de desenvolvimento da larva. sendo maior no terceiro instar. com 279.1 pulgões. representando aproximadamente 82.0% do consumo total. Observaram-se uma duração de 11 dias para. a fase larva! e uma viabilidade de 100% em todos os estádios de desenvolvimento. Para os três ínstares e fase larval. constatou-se maior consumo e duração em função do aumento da densidade de presas. Verificou-se uma resposta funcional Tipo II para. todos os ínstares. Constatou-se. para larvas de segundo e terceiro instares. o menor tempo de busca. e o primeiro instar apresentou a maior tempo de manuseio