Constraints on Non-Singular Cosmological Models with Quadratic Lagrangians

We consider the generalized set of theories of gravitation whose Lagrangians contain the term $R^{2}$ : $L=\sqrt{-g}(R+\beta R^{2})$. Inserting the RW metric with an imposed non-singular and inflationary behaviour of the scale factor $a(t)$, and using a arbitrary perfect fluid, we study the properties of $\rho$ and $p$ in this context. By requiring the positivity of the energy density, as well as real and finite velocity of sound, we can obtain the range of values of $\beta$ that ensure the inflationary behaviour and absence of singularity.Comment: 11 pages, RevTeX, 3 Postscript figure

Revisiting Import-Substituting Industrialisation in Post-War Brazil

This article reassesses the classic period of Import-Substituting Industrialisation (ISI) in Brazil between 1945 and 1979. New data presented here show that Brazilian industry achieved significant labour productivity growth during the post-war years and became more technologically sophisticated, when measured by manufacturing exports and evidence of specific industries and firms. We also found that Brazil’s labour productivity growth lagged behind what was achieved in other industrialising and developed countries from the mid-1970s. Technological advances were slow and uneven, and most firms relatively backward. Overall these results suggest that a highly heterogeneous structure became a major feature of Brazilian industrialisation, rather than widespread inefficiency and technological stagnation as argued by the dominant interpretation of ISI in Latin America.Import-Substituting Industrialisation; Productivity; Technology; Brazil; Latin America

Newtonian Approach to the Matter Power Spectrum of the Generalized Chaplygin Gas

We model the cosmic medium as the mixture of a generalized Chaplygin gas and a pressureless matter component. Within a neo-Newtonian approach we compute the matter power spectrum. The 2dFGRS data are used to discriminate between unified models of the dark sector and different models, for which there is separate dark matter, in addition to that accounted for by the generalized Chaplygin gas. Leaving the corresponding density parameters free, we find that the unified models are strongly disfavored. On the other hand, using unified model priors, the observational data are also well described, in particular for small and large values of the generalized Chaplygin gas parameter $\alpha$.Comment: Latex file, 5 pages, 11 figures in eps format. For the proceedings of the conference Dark Energy and Dark Matter, 7-11 july 2008, Lyon, Franc

Ruling out the Modified Chaplygin Gas Cosmologies

The Modified Chaplygin Gas (MCG) model belongs to the class of a unified models of dark energy (DE) and dark matter (DM). It is characterized by an equation of state (EoS) $p_c = B\rho - A/\rho^{\alpha}$, where the case $B=0$ corresponds to the Generalized Chaplygin Gas (GCG) model. Using a perturbative analysis and power spectrum observational data we show that the MCG model is not a sucessful candidate for the cosmic medium unless $B=0$. In this case, it reduces to the usual GCG model.Comment: Latex file, 7 pages, 6 figures in eps forma

Quantum Isotropization of the Universe

We consider minisuperspace models constituted of Bianchi I geometries with a free massless scalar field. The classical solutions are always singular (with the trivial exception of flat space-time), and always anisotropic once they begin anisotropic. When quantizing the system, we obtain the Wheeler-DeWitt equation as a four-dimensional massless Klein-Gordon equation. We show that there are plenty of quantum states whose corresponding bohmian trajectories may be non-singular and/or presenting large isotropic phases, even if they begin anisotropic, due to quantum gravitational effects. As a specific example, we exhibit field plots of bohmian trajectories for the case of gaussian superpositions of plane wave solutions of the Wheeler-DeWitt equation which have those properties. These conclusions are valid even in the absence of the scalar field.Comment: 10 pages, RevTeX, 3 Postscript figures, uses graficx.st

Graceful exit from inflation using quantum cosmology

A massless scalar field without self interaction and string coupled to gravity is quantized in the framework of quantum cosmology using the Bohm-de Broglie interpretation. Gaussian superpositions of the quantum solutions of the corresponding Wheeler-DeWitt equation in minisuperspace are constructed. The bohmian trajectories obtained exhibit a graceful exit from the inflationary Pre-Big Bang epoch to the decelerated expansion phase.Comment: 8 pages, RevTeX, 4 Postscript figures, uses graficx.sty. Added more text and reference